Sexual orientation is definitely fluid. I've been lesbian most of my life, but a couple years ago, I "experimented" with a man, developed a relationship with him, and a couple others, and now am solidly "bisexual."
(Well, I don't really subscribe to binary gender, as there a lot of people who are genderfluid or genderqueer who I'm attracted to.)
But to address some points in your original post-- anal sex is definitely not a gay thing. You, as a man, have a wonderful thing called a prostate gland, and you can get something out of anal stimulation that people without that gland cannot enjoy. You should experiment with it.
As for sexual orientation, what other gender markers turn you on? Beards, hairy chests, broad shoulders? Rough skin and funky smells? Rumbly voices?
As much as my primary orientation is women, the truth is that I'm very much attracted to big bear type men, with the big hairy muscle-bound bodies-- not so much what I'd expect from an erstwhile lesbian, but there you go.