This forum has some of the weirdest questions... Things that I never even give a thought.
I don't think in back or in front has anything to do with whether or not it's a gay act. If you get hard looking at another guy, you probably have a gay or bi tendency. If you are horny and your GF is out of town, and a gay guy wants to blow you and then gets you to poke him in the arse while you're drunk and thinking of an exotic chick, that probably doesn't make you gay. Personally, to be graphic, no matter how horny for a hole to stick it in, I don't want some other dude's poopchute near me, so I'm not going to go that way. And just for the record, when my wife is out of town, I wait for her to come back. I was just using that as an example.
Charles