This applies to the rank and file, the military elite, and the King himself.
Was homosexuality common among the men who made up the rank and file of the military (the phalanx battalions, shield bearers, companion cav), or was it limited to the royal pages of the Macedonian elite?
And in regards to Alexander, it is widely acknowledged he had a sexual relationship with the eunuch Bagoas, but his relationship with Hephaestion isn't as obvious. What is the most likely consensus regarding Alexander's sexual partners during his lifetime?
Homosexuality in the ancient world was actually rather commonplace - it was not about who your sexual partner was, it was more about who was the more powerful person in the relationship was.
In the Greek armies, (contrary to what 300 says) there is extensive evidence for pederasty having occurred on a regular basis. In fact, this was considered a normal part of training within the military, which Alexander would have been involved with, since there was an older man known as an 'erastes' and a younger man known as a 'eromeneos'. In Sparta, this was taken to a whole new level, with this being a standard part of training in the agoge by a male mentor.
As well, there is evidence (particularly prevalent in the Iliad about a relationship between two men - that of Achilles and Patroclus in particular), which gives credence to the idea of a relationship between Hephaestion and Alexander.