It makes sense, I kind of think the same about my brother & I. As in, "if we had never messed around, would I be bi now?"
It started after our Dad died, when he moved into my room because I kept having terrible nightmares. I don't remember
exactly how it started, like how he initiated etc, but he was the elder brother and I'm pretty sure it something like him saying "my friends told me about this thing at school, want to try it out?" and as I felt bad that he had been forced to share a room with me despite him not wanting to, so I said yeah, hoping he'd forgive me.
I remember it just started off as blowjobs, me sucking him. We used to call it something really weird so that we could talk about it in front of other people without them catching on.
Over time it progressed into anal, though we'd always be really coy about everything. It would never really be "come over here, and give me a BJ?", it'd be him subtly pulling his shorts down (or whatever he wore to bed) and then me just going over and doing it or me pretending to be asleep, but subtly having my shorts (or whatever I wore to bed) pulled down a little and him coming over and sticking it in me.
He did suck me off sometimes, but I never really enjoyed it. I tried to do him in the ass but I really had no idea what I was doing, so I didn't really enjoy that either so didn't do it often at all. Although now I know what I'm doing, I still don't really enjoy it (although I would say that I am a top). I think I do it because I know, from my experiences, how good the other person could be feeling, if that makes sense.
It ended about 4/5/6 years later when our mum decided that I was old enough to not have nightmares, so she let my elder brother move back into his own room.
We've never mentioned it since, but I'm the only one of our brothers that he never really gets mad with, so I do wonder if its because he remembers what we did together. Or maybe he just doesn't mind me.
I've had emotional + sexual relationships with men + women since, but recently I've started to fantasize about my brother again and its just weird. The men I like are kind of the same type as him, which is why I think he played a somewhat significant role in me being bi.
first time i've ever talked about this