Though I was mostly attracted to girls, I went through such a period. I never acted upon it. I missed two opportunities to do so. Not by my fault, but due to adverse circumstances (IMO fortunate in one case, unfortunate in another).
I’ve been brought up in a small backward village, and homosexuality or bisexuality wasn’t particularily popular or trendy. And also rarely watched TV, and it didn’t mention it to anybody before my late teens, so it had nothing to do with being “cool” (anyway, being bisexual still isn’t particularily cool amongst boys), or with exposure to medias, or with seeking attention.
I’ve absolutely no clue when I discovered that homosexuality even existed. I think I discovered I had some sexual interest in boys at the same time I discovered I had a lot of sexual interest in girls. What I do remember is that when I was about 12-13, I read a “contraband” sex ed book (I borrowed it for the pictures, mostly) that mentionned that young teens are often, as you said “confused” about their sexuality and can be, generally temporarily, attracted to the same sex. So, I thought “fine, that’s normal” and it didn’t bother me (though, as I said, I most certainly didn’t mention it to anybody).
Later, say when I was around around 17 or so, perhaps, I assumed that I was bisexual. At this time, I was hanging out with leftist, politicallly aware (as much as you can be aware at 17, at least) and vaguely active (when we weren’t smoking pot) friends. So, it wasn’t an issue, and indeed, at this point, it was rather “cool”, at least in our micro-world, so I didn’t hide it. That’s also when I missed the two opportunities I mentionned above (the first when I was 16, the second when I was 18).
However, the more time passed the less I had an interest in boys. Interest in girls stayed at a high (and increasing) level.
Nowaday, I can only define myself as heterosexual. Not only being attracted to someone of the same sex became extremely rare (like in one time every other year at most, while I notice two dozens of attractive girls and women each time I ride the metro), but also when it happens, it’s not really a sexual attraction. Rather a strong emotional one. I’m not really interested in having sex with any man, now, and there’s only one I can’t think of right now I would like holding in my arms (as opposed to approximatively 128 457 women). It’s conceivable that I could have sex or fall in love with a man, but it’s very, very unlikely.
I discovered even earlier that I had an interest in some kinky stuff, while reading italian “fumetti” secretely “borrowed” from my older brothers but it’s another story entirely.