Colin was not gay. Period.
I have nothing against Colin being homosexual..in fact it could have been a really definite twist but from what I think, despite some allusions, he is certainly not one....
Here is my explanation....
In the early part of the film, during the rugby match, Colin makes some harsh comments about firefighters being homos which sort of explains his distaste for the same behavior and it is a bit unclear whether he himself is one or not.
During his first day in SIU, he observes a woman's hips and even whistles at then. He stares at them again and he certainly does not look as if he is queer or something.
Of course, there are moments where he is unable to get it up and perform but did you notice the moments where he really gets all hot and turned on- passionately kissing Madolyn just before Costello calls him up or that scene towards the end- when he grabs her and starts kissing her after she shows him the X-ray?
You can say safely that Colin was at times impotent and the compulsive liar that he was, he even made a huge thing of his sexual life (yeah, it is working. Overtime)but my feeling is that his sexual performance was directly affected by his life as an insider.
He was tempted by the security and prestige that his job as a cop was offering him and he was sort of confused- that if he goes back to Costello, where does it lead to- the same grubby life from which he had been rescued in the first place? To hold all that temporary security and sense of luxury together, he was at times extremely anxious and it was this anxiety that showed up in places.
His initial night with Madolyn goes wrong for the simple reason that the pressure is building on him- he is tipping Costello off, he is trying to cover up murders made by the gang and all of that puts a pressure on him.
Whereas, in that scene when he starts kissing her while at home before Costello calls, he feels at temporary peace and security and he relishes it perfectly.
The same is with the scene in the end- he feels that he has nothing more to lose- Billy's identity is erased, noone will harm him now, Costello is gone and he can now start a nice family. It is this idea itself which sparks his sexuality.
What do you think?
You can say that