Once you experience a gorgeous erection pressing against your anus, through your anal canal, and ultimately captured within the folds and abyss of your rectum there's no looking back. Your body desires and craves anal pleasure and penetration...
I like to think of it as a forbidden place, like its wrong,dirty and naughty. My wife liked to be anally fingered whilst I was penetratrating her pussy, well she never stopped me from doing it, I used to like feeling my cock thrusting in her pussy.
When I rejected my boyfriend's request for anal sex at university, he seduced me to explore anal pleasure by offering me a slow, sensual personal tutorial of how to enjoy my anus and rectum. It still became a rather naughty exception to vaginal penetration -- but I never looked back and like the sexual tension of a gorgeous erection in my behind.