Can sex with my sister make me cheat?

This is a young man's tale who has a girlfriend and a great sex life with her, but constantly cheats on his girlfriend against his wish which makes him think it might be as a result of his past sexual encounter with his sister. I sorta stumbled on this story and decided to share it with you and please if you have any word of advice, question or comment, do feel free to leave them here.

I've got a great girlfriend and I'm very happy with her, yet just the other night I had sex with another girl I met out clubbing. I can't figure out why I did it.

I'm 29 and my girlfriend is 26. We'v been together for three years and our relationship is fantastic. Our sex life is great too. I promised myself I won't cheat but seem to end up having a fling or one-night stand every two or three months.

I get chatting to other girls when I'm in pubs or clubs and can't resist once I realise I'm in with a chance. I met this latest girl in a pub when my girlfriend was away visiting her mates. We had a few drink, I offered to walk her home and she invited me in. We'd only just got through the door when she started kissing me passionately. We ended up having great sex right there on her hallway floor. Like the others, I don't love her and look at it as just a bit of fun.

I'm straight but I'v even cheated with gay men as I find them easier to hook up with than women. I used to be addicted to Phone sex and often ran up huge mobile phone bills but I'm over that now. I feel week and pathetic. I want to wipe the slate clean and be completely faithful. My girlfriend deserves so much better from me.

I used to have consensual sex with my sister when we were teenagers. Do you think I am just trying to find something to replace the thrill of breaking that sexual taboo?