Confused about my girlfriend.

My girlfriend and I have been going out for about a year and two months.
The issue that I am having is that i do not feel like I am attracted to her anymore.
I know this seems very shallow of me but I am constantly thinking/checking out other girls.
Even though i am not attracted to my girlfriend, i feel like i still love and care about her a lot.
When we argue, and she begins to cry, even if its not my fault my first thought is to hold her tight because i hate to see her that way.
I never would want to do anything to hurt her but I sometimes i wonder who else is out there for me.
She is my first real girlfriend, shes 21 and im 19. She was also my first, but i wasn't her first.
Anyway I am really confused on what I am feeling right now. Sometimes i think about breaking up with her but I could never hurt her.
Not to seem conceited but i know shes deeply in love with me and very attracted to me.
Is this something i can get over as our relationship goes on or will i regret it later on?
Any help would be really appreciated, and if you have any questions please let me know.
Thank you.