I am bisexual. When I first started having sex with men (age 22) I had no desire to have any kind of anal sex. I told who ever I was having sex with upfront that I was into giving and receiving hand jobs and that I really loved giving and receiving blowjobs, I would also tell them I loved sucking a man's cock and having him cum in my mouth and swallowing his cum.
Years later (age 26) when I became involved with a very good friend who was gay. Having regular sex with him changed the way I felt about anal. One time he was giving me one of his always excellent blowjobs when he suddenly lifted both of my legs up in the air (I was sitting on his couch with him kneeling on the floor in front of me). He took his mouth off of my cock and started licking my asshole. I was startled but I decided to let him lick and kiss my asshole because it felt absolutely amazing. This went on for a good 30 minutes. It was pure ecstasy. and in some ways was more pleasurable than having him suck my cock. He didn't need to ask me if I liked it because my groans and squirming told him that I loved it.
After that session I started thinking about having anal sex with him. The more I thought about it the more I knew I wanted him to fuck me. Because we were friends and he knew I was an anal virgin I knew he would be gentle. I had absolutely no interest in being a top so I focused on being a bottom. Could I actually let another man fuck me? It was one thing to give a BJ or HJ to a man and have him reciprocate but letting another man put his cock in my ass was a huge step in my bi-curious experiences.