Don't sweat it dude, it happens. I think about different girls all the time. The girls I wanted to date, the girls I wanted to marry, hell I even think about girls I wouldn't touch again with a six foot pole. Then I crack open a beer and forget about it.
@GohantheThird I don't drink but I have my work, Gym and my games to take my mind off. I also think about other girls too but the first love is different.