Hai
I'm 19 and have been in a on/off relationship for 4 years its been on for the last year and a half. But I've cheated on her whill we were together and told her, our relationship is stronger and better but the trust issue is a big problem. I'm committed but always start to feel things for our close friends this is the 3 time I've started to get feelings for someone else? What should I do?

If you're wanting to have sex with all sorts of other girls all the time, then it sounds to me like you're really just not ready for a committed relationship. If you're developing feelings for other girls, then there's probably something missing from your current one. Either way, I really don't think it's fair to your girlfriend to keep on going as you are.
My advice: Talk to her about these feelings you're having, and go from there. You're very young, still, so to be honest, a break-up is most likely in order. Sounds like you need to shop around, still.

Its okay to have feelings for others, that's human my young friend, but its not okay to act on them, especially when you are trying to rebuild trust in a relationship that you have already cheated in. Stay within the boundaries of good behavior, and keep thse fantasies of her friend to yourself.

It is not fair for either of you to go through all this again. It sounds like you want something different than a relationship. That is fine but you owe it to your girl to break it off before something bad happens... again.

Since this relationship has been on and off for 4 years, and you are only 19, chances are you have not had much opportunity to date other people or be in other serious relationships.

It might be best to take a break from being in a committed relationship until you truly want to be there. As was said, it is normal to find other people attractive, but if you are finding yourself seriously thinking about being with other people, time to end the relationship and allow yourself to date others.

Part of dating is to have the chance to get to know different people and learn what you like and don't like. Maybe you need more opportunities to do that before you get serious about someone.