I'm not sure the Colonel - Chris Cooper's character - was gay
First few times I watched it, I assumed he was a closet gay. But he's from the military - where guys are close. I got impression from movie he's now ex-military. He doesn't have relationship with wife, kinda interacts with his son - who he finds out is gay (but not actually), then finds out his neighbor (Spacey) is gay (but not actually) and the two gay neighbors. Seems like he'd have felt like a lonely guy, all those men around him but none for him to feel close to.
No, I'm not sure he was gay - I think he was very hungry to be close to males though - and so he finally succumbed to what he thought every other guy around him was doing to be close to another male.