Hephaestion, son of Amyntor, had been a close friend of the King since boyhood. He had been with Alexander as a teenager at Mieza, when Crown Prince was educated by Aristotle. Romantised accounts compared the two with Achilles and Patroclus. Whether they were lovers, as many modern writers like to assert, is not entirely clear. But Alexander certainly promoted Hephaestion's career despite the fact that he seems to have possessed poor leadership qualities and little military skill. He was nevertheless a gifted organiser and Alexander left many matters of logistics - supply, transport of equipment, bridge-building, and the founding of settlements - to him.
By the time the army reached India, Hephaestion's promotion had brought about friction with other officers, especially the fine soldier Craterus. At one point the two came to blows in front of their respective troops and Alexander had to intervene.
Waldemar Heckel "The Wars of Alexander the Great" Osprey Edition
That 'fine soldier' speaks of an unacknowledged contempt for the non-military man. Craterus, it would seem, is the bluff soldier who got where he was by his own integrity whereas Hephaestion got where he was by devious and subtle means.
I wanted to write a defence of Hephaestion but the accusation of nepotism won't go away and Alexander's 'you are nothing without me' doesn't help. It seems to be interpreted exclusively to mean that Hephaestion alone had achieved his position by Alexander's favouritism. Equally though, Alexander might have meant that all of them had only got where they were because of him but because we don't have the details of the quarrel, we cannot be certain.
Yet if we are to assume Alexander's quote was directed exclusively at Hephaestion, that might hint at reasons for Hephaestion's reputation for quarrelsomeness. Evidence for this reputation doesn't appear until after Hephaestion's rise to prominence following Parmenion and Philotas's removal. If it was felt that older, better, more experienced soldiers than Hephaestion should have been promoted to the vacant commands, he may well have had to face accusations of favouritism and an undercurrent of jealousy, despite Heckel's assertion that no one mentioned the nepotism. Jealousy may have been behind the quarrel wth Craterus, or it may simply have been that power went to Hephaestion's head and that he had to be reminded by Alexander who was king. Yet we have nothing to judge these quarrels against. The earlier quarrel with Eumenes is only mentioned because it was followed by the one Alexander was asked to intervene in. Because Alexander didn't become involved in them that we know of, we don't hear about the undoubted feuds and jealousies that must have existed amongst Alexander's other officers, so Hephaestion's reputation for quarrelsomeness may be disproportionate.
Hephaestion may not have been a first rate battle commander, but that doesn't make him a coward or incompetent, or worthy of contempt. Alexander would not have repeatedly given him independent commands had he been incapable. These commands may not have been as glamorous as leading a decisive charge in a big set battle, but that does not mean that they were any less important in achieving the success of Alexander's expedition. Hephaestion's promotions did not harm Alexander's success, and in appointing him as chiliarch, Alexander may well have recognised that the administrative functions of the Great King required more attention than he could, or would, give them.
Hephaestion was no Sejanus. He may have helped push Philotas off the cliff, but he didn't put him there in the first place. He may have bent Alexander's ear about Eumenes and Eumenes may have been quaking in his boots, but he was neither punished nor lost his position. Ultimately then, Alexander's favouritism for Hephaestion caused no more harm than appointing any other of these ambitious, ruthless men to positions of immense power. We don't hear of him hoarding money like Eumenes, or appropriating funds like Harpalus, or shipping sand like Craterus and Perdiccas. So what was the harm in Alexander's favouritism? All kings and rulers have favourites and friends in positions of power. They rely on them to carry out their will, otherwise they would have to coerce people. Just because Hephaestion did not come from a powerful family and did not inherit a position of power does not mean that he did not merit that power or does not mean that he didn't work just as hard as anyone else to hold onto it. Nor does it mean that he deserves contempt for not being a brilliant soldier who could strut his macho stuff in retellings of the big battles.
Enough. Sorry for going on a bit.