(21M) Since I was young I have tried to always do what is ethical. I think that is because my mother and father always raised me to be kind. Sometimes I want to do whats ethical but my mind pulls me like a semi truck up a hill. So I am confused.

I have been dating my gf (22F) for 3 years now. I cheated on her 1 year ago, told her immediately and we stayed together for 2 months before ai broke up with her to mess around with a friend. After moments of clarity I called her back and we got back together without a hich. I feel like I lack alot from my relationship with her. The experiences I have without her (sexually) are my favorite. I can’t help but think of other women especially the ones i’ve been with in the past. She is a great girl and I love her but I feel like I don’t see much of a future with her even though there isn’t much wrong in the relationship.
Recently after thinking of one of my exes she called me and she has a bf. We talked for 5 min before I had to hang up but I can’t stop thinking about her. I know my feelings are routed in sex but I feel like I need to leave my current relationship to explore life while im still young. 

Advice?