Ernst Fleischl von Marxow (1846-1891), was an Austrian Jewish physiologist and physicist. Already 34 years old, Fleischl became a full professor at the University of Vienna. (Compare his achievement with Freud's (complaints about antisemitism in academia.) Unfortunately, after the amputation of an infected thumb, Fleischl was in a constant pain, and became a morphine addict.
Fleischl was exactly the kind of person, Freud was looking for, a wealthy academic who could help him get ahead in the academic life without wasting his time on learning, as well as provide him with money.
Freud was a human parasite, always attaching himself to successful people with financial means, whom he admired but couldn't compete with. This was also the case with professor Fleischl. Thus, Freud wrote in his letter to his fiancé, Martha, of June 27, 1882, I wasn’t satisfied until we became friends and I could take a pure delight in his ability and worth.*
How the parasite managed to attach itself to its host?
At the time, there was an epidemic of syphilis in Vienna, and a common, although mistaken, belief was that one could not catch the disease by anal sex. No wonder, that gay sex was a valuable asset, and Freud could offer it to his benefactors, like doctor Josef Breuer, professor Ernst von Fleischl-Marxow, and others, who could offer him both academic and financial support that Freud badly needed.
Thus, among others, Freud attached himself to, Dr Josef Paneth and Ernst von Fleischl-Marxow who both had private means, and [to Dr] Josef Breuer with whom he was running up a steadily growing debt.**
(No doubt Freud had a sexual relationship with his sugar daddies, Breuer and Fleischl. Whether also he was serving Paneth's sexual needs is uncertain, but not impossible.)
* Crews, Frederick, The Making of an Illusion, (2017, p.  76).
** Clark, Ronald, The man and the cause, 1990, p.  58.

All of Freud’s sugar daddies supplied Freud with loans that were never to be repaid. In fact, Freud only survived thanks to the alms from his benefactors. Freud had no scruples when it comes to asking for money. And he was always scavenging for more "loans". He even joked about his dependency on his “friends” money, informing Martha, on August 28, 1883, that he couldn’t get any “loan” since his, ordinary bankers were not at home. (1)
Over the years, Fleischl was one of his most generous "bankers". We don’t know the full extent of Freud’s financial exploitation of Fleischl that went on for many years. The scarce available information can be found in the published letters mentioning Fleischl.
Thus, on October 25, 1883, Freud asked Fleischl, to give me just enough to travel to Hamburg. As Freud reported to his fiancé, fortunately, This was granted. (2)
And, on March 10, 1885, Freud informed Martha that, when I have come to the end of my money, I will go and see him [Fleischl]. I wonder if he will lend me anything. (3)
Already two days later, on March 12, as Freud reported, Fleischl, slipped me the money secretly. (4)
Only three weeks later, Freud complained that, on this occasion, he, couldn’t get anything from him, (5) because there were too many people present.
Having returned from Paris, where he was on a scholarship, Freud confronted Fleisch asking why he didn't send him money. As Freud recounted in the letter of July 4, 1886, Fleischl has apologized repeatedly about the money he didn’t send. (6) Apparently, Fleischl felt guilty about not providing Freud with the money Freud was “entitled” to.
(1) Freud, Sigmund, The Letters of Sigmund Freud, 1853-1939, (1960, p. 49).
(2) Freud, (1960, p. 73).
(3) Crews, Frederick, The Making of an Illusion, (2017, p. 138).
(4) Crews, (2017, p. 128).
(5) Crews, (2017, pp. 128-129).
(6) Crews, (2017, p. 137).

Already eight years before Fleischl's death, Freud was anticipating his "friend's" death. this is how he informed his fiancé, Martha, on October 28, 1883, His downfall will move me the way that the destruction of a holy and famous temple would have touched an ancient Greek. And Freud confessed: I love him not so much as a man but as a precious achievement of creation. Tantalisingly, Freud added, And you do not really need to be jealous. Indeed, if she knew about the full extent of Freud’s love, she would. (1)
Notably, Freud introduced Fleischl to cocaine, as he claimed, aiming to alleviate the former's morphine addiction.   As he recounted in his letter to his fiancé of April 21, 1884, he was going to try cocaine on Fleischl condition, following withdrawal of morphine. (2) Actually, looking for a revelation he could exploit for his own fame and position, Freud used Fleischl as his guinea pig. As a result, besides morphine, Fleischl also became addicted to cocaine.
Bizarrely, Freud was already considering Fleischl money his own. Apparently believing that he would inherit Fleischl, he complained to his fiancé on May 21, 1885 that, Fleischl has already spent 1800 marks on cocaine. A good part of our fortune, isn’t it? (3)
Apparently planning ahead, Freud wrote to Martha that Fleischl's death would solve his financial obligations to Fleischl stating, If [he does lend me the money], he may no longer be here when we need to think about paying it back. (4)
The fact is that having become addicted to both substances, Fleischl was becoming weaker by the day, thus fulfilling Freud’s death wish towards him. Even though Fleischl died first in 1891, thus, giving Freud lots of time to repay the “loans”, no doubt making Freud a happy debtor, he died before he could be repaid. (5)  Not that Freud even tried.
(1) Freud, Sigmund, The Complete Letters of Sigmund Freud to Wilhelm Fliess, 1887-1904, , (1985, p. 71).
(2) Freud, Sigmund, The Letters of Sigmund Freud, 1853-1939,  (1960, p. 108).
(3) Crews, Frederick, The Making of an Illusion, (2017, p. 133).
(4) Crews, (2017, p. 129).
(5) Jones, Ernest, Sigmund Freud: Life and Work: The Formative Years and the Great Discoveries,, (1953, p. 161).

Even though claiming he was Fleischl’s friend, Freud wasn’t always behaving towards the former in a friendly manner. Thus, In the Address to the Psychiatric Society, Freud sharply criticised Fleischl, his immediate superior in the Institute, to whose position he might have hoped to succeed.
Moreover, Freud, resorted even to the method of personal psychological interpretation. As his biographer, Jones, points out that, it is hard not to associate it ... with the dissatisfaction and frustration at having to leave the Institute. And Jones explained that, It is an example of the ambivalent changes between friendliness and hostility, typical for Freud.
Today a friend, tomorrow a deadly, (or a dead) enemy. Thus, Freud confessed in later years how he had secretly cherished the thought that his advancement would be favoured by Fleischl’s death. (1)
Likewise, Freud’s doctor, Schur, in his Freud biography, confirmed that Freud, wanted ... Fleischl ... to die.(2)
Now comes the great lie. In his Autobiographical Study, Freud claimed that, it was generally thought that I was marked out to fill the next post of Assistant that might fall vacant there. (3)
But as Jones pointed out, the head of the institute, professor, Brucke had no intention of parting with either of his two valuable Assistants, Fleischl and Exner. (4)
No wonder, that Freud was keen to see Fleischl dead, if he was bizarrely believing that Fleischl death would allow him to take the latter's vacated place. Without doubt, the cocaine treatment devised by Freud was one of the means to hasten Fleischl's death, and it worked. As Freud revealed in the dream book, The misuse of that drug had hastened the death of a dear friend of mine (5) conveniently "forgetting" to mention that he not only introduced Fleischl to cocaine but also gave him injections of the drug.
Fleischl died in 1891, when Freud was 35 year of age, but his death didn't result in Freud's return to the Institute. Being ambitious wasn't enough, Freud was, simply put, incompetent to take Fleischl's place.
The last known mention of Fleischl appears in the letter of May 30, 1886 in which Freud mentions that he, helped to bring him [Fleischl] through one of his anxiety attacks. (6) What happened during the five years leading to Fleischl’s death is not known. Likewise, it is not known who administered the last cocaine injection that presumably ended Fleischl’s life. Actually, Freud was accused of having deliberately assassinated his friend Fleischl-Marxow in order to eliminate a rival. (7) As a matter of fact, the claim appears highly plausible.
(1) Jones, Ernest, Sigmund Freud: Life and Work: The Formative Years and the Great Discoveries, (1953, p. 62).
(2) Schur, Max, Freud: Living and Dying, (1972, pp.341-2).
(3) SE 20, pp. 9-10.
(4) Jones, Ernest, Sigmund Freud: Life and Work: The Formative Years and the Great Discoveries, (1953, p. 61).
(5) SE 4, p. 111.
(6) Crews, Frederick, The Making of an Illusion, (2017, p. 238).
(7) Roudinesco, Elizaheth, Freud in His Time and Ours, (2016, p. 435).

In the dream book, there are several references to the deceased professor Fleischl. Thus, Freud recounted, the recollection of another dear teacher [Fleischl]. Significantly, in this context, undoubtedly referring to his own mental state, Freud mentions insanity, (1).
Indeed, Freud's insanity, of which he was aware, manifested itself, among others, as a pathological ambition.
Analysing his alleged “Non Vixit” dream, Freud admitted that he harboured a death wish against Fleischl. Claiming that it was doctor Paneth, who replaced Freud at the Institute, that wished for Fleischl to die, Freud confessed that, Not unnaturally ... I myself had nourished a still livelier wish to fill a vacancy. (2)
And what is a still livelier wish other than a wish to murder Fleischl. Remarkably, Freud didn't consider his "livelier wish" unnatural!
Bizarrely, Freud wasn’t hiding that he was, sacrificing to my [pathological] ambition people whom I greatly value. As he elsewhere admitted, his, craving to be addressed with a different title [of a professor] … showed a pathological ambition. (3) 
The situation was no different when he craved Fleischl’s assistant's position at Brucke’s institute.
As it is apparent, Freud's pathological ambition manifested in the elimination of the people, who, he believed, were an obstacle to his career.
(1) Freud, Sigmund, The Interpretation of Dreams, (1913, pp. 173-174).
(2) SE 5, p. 484.
(3) SE 4, p. 192).