Hmmmm for me I think it's a story that took a lot of years of gradual changes. I think I always had intruding thoughts about guys when I was horny though. I consider myself heteroflexible. Outside of being horny I dont find other men interesting.

Anyway, at some point as an adult I read an article about prostate play and the pleasure it can bring. I put my prejudice aside and bought some butt plugs and dildos and started experimenting on myself. A bit later I started being interested in bi porn and soon after that I found myself blowing dildos, watching gay porn, etc...

Fortunately for me, my partner (woman) has absolutely no problem with this.