My first few sexual experiences were with other boys; Age 13 I fooled around with a close friend for a year or so and we pretty much did everything up to and including bum sex, which I found uncomfortable and unpleasant so we never tried it again. Frankly at that age I was so horny I'd have put my penis into pretty much anything, and of course at that age parents will let you sleep over at another boy's house but not another girl's so it was kind of inevitable.
These days I think I'm in the 'potentially bi' category, in that I'm in a happy monogamous heterosexual marriage, so I'm not in the market for anything else, but if the worst were to happen and we were to split up, it wouldn't be *impossible* for me to imagine being in a same-sex relationship (no bum sex though, ugh). But mostly I just like lady parts too much and I think I'd miss them.