Either keep it what's in your pants between you and your GF... or break up with her to get something else.

If you're not happy because of something superficial like an ass? You can't control what gets your motor revving... but you can control not being a cheater and a horrible person.

Either stick with the relationship and stop looking at other girls... or go chasing the other girls and break up with your GF on good terms - not after breaking her heart.