How can I just focus on the girl I'm with?

Well if it makes you feel any better, I'm the same way when I have a boyfriend. You're not alone. =]

U don't seem CONTENT in which it has everything to do with you and nothing to do with the girl's you choose to be with. Your not the only guy that thinks this way ( not the only person in general) fact of the matter the grass at times does seem greener, but that's not say it is. Its not about being with one girl and letting the others go , it's about being with one person that brings some sense of happiness in your life and not needing any replacement's. There's a saying I learned long ago '' What's good to you isn't always good for you. '' With that being said if you want to make something work with someone make it happen. However if you have any doubt's in your mind let it go. Funny thing is you may just not know what you have until it's gone. NOW I think we've all heard that one a time or 2. You don't need any advice you just need to do the right thing I think we both know what that is.

You need more cowbell, haha, lol, no seriously don't know where that came from, anyways that's something that I think that is going on, you asked a serious question, and at first I didn't take you seriously. I needed more discipline; not cowbell. lol, enough, okay, but there's a serious answer in all of this. (old SNL, lol)

The girl your dating, it's like, you've only known her for the amount of the time that you dated her. She lived through a lot of experiences before that. There are layers and layers of a person to uncover from their childhood until the time we meet the person we are to date. We can't get to know what makes them an individual in a moment, a day, or a month, etc.

I get the feeling that one of two things are happening when you enter a relationship
1: there's a boost in your self esteem and other girls-other than your girlfriend-notice(but they don't know you have a girlfriend, unless you're with her) and this makes you presence stand out more because of the boost in self esteem, that is almost unnoticeable at times, but it makes you think, whatever.

or

2: there's a feeling of entrapment from pressure that's not normally there when you're not in a relationship so the other girls look like dating options.

But you know your girlfriend on a deeper level than the girls you see. And you chose her to be your girlfriend, focus more on what makes her the one you chose - what makes her different, what makes her (on her own, lol, w/out you in a sense) feel brave, what makes her feel scared. You see where this is going, it's about discipline to a passionate commitment, and enjoying it for what it's worth; Experiencing it for the whole and not just getting your feet wet.