I was keeping my GF company while she studied, but an old friend who I used to have mutual love with wanted to hang out. My GF was irritated, but I went to see this other girl anyway and drank with her. Well we ended up kissing, and i feel bad I cheated but I used to love this girl so much and still care about her. My current GF is incredibly sweet n understanding n doesn't deserve this...
The girl I kissed just told me shed wait for me...
This is the second time cheating...
I told myself the first time that I would never cheat again because it wasn't worth lt and didn't tell my GF.
This is the second time n I just feel like shit.

Am I too immature for a relationship?
What do I do? Is it best to keep this all a secret, (what she doesn't know won't hurt her)?

Wow man you love her enough to cheat on her? How is that love?

Okay so maybe you were weak once, you were tempted, but to do it again? When you went out drinking with that other girl what do you think was going to happen? Avoid that kind of temptation man.

This is the kind of thing that gives guys a bad rep and destroys relationships.

Obviously don't tell her and if she asks, deny to death. Oh and if you really love this girl (which I doubt) then never, ever, do it again

/facepalm

The BEST thing to do is to break up from your GF asap and start dating.
Tell the friend you are only looking for something casual and if she accepts continue seeing her.
You are obviously not ready for a relationship or haven't found yet the right girl.