Replying to i need an advice

i got a girlfriend i love. she 's perfect to becaome a great wife. but there 's this girl, i think she wants me, and SHE IS SO HOT! she would probably make the worst wife ever (working, independant, no kids, ...), but damn! i can get her body out of my head!
do i have to leave my girlfriend for the best piece of sex ever (maybe life long sex with her, but it would be our only common point) our should i put my penis in my pocket and stop thinking about it?