I first realized that I was bisexual when I allowed my younger brother to insert his erect penis into my rectum and fuck me until he came in me and pumped his seed deep into my willing body where I wanted it in there and that it belonged in there.
This goes for anal sex in general. Throw in the fact that the orifice is traditionally tabu and the smell, which everyone claims to hate but secretly love their own scent, and knowing the person probably shit hours before your penis was inside them.
"Stay inside me please!" the bottom says. Staying inside the person you just came in is truly the most special union, the bond is so erotique and emotional. The ultimate is french kissing the bottom after you've cum, penis still inside, and just tasting his mouth as his asshole clenches your penis.
Whenever he wanted to fuck me, I allowed him to do it. But he always came in my ass-pussy, never in my mouth although I did sometimes suck on him to get him even harder.