You say you like this girl a lot and have a lot of fun together. Is that because you are hitting a 19 year old and know your opportunity to do this is running out?
Seriously, what do you have in common with her? I'm 25 myself and find 99% of college girls to be downright annoying as hell now. Either she is very mature for her age or you're very immature for yours. Seeing how you still associate weekends with alcohol I'd have to go with the later.
I'm not trying to rip you apart so don't take it that way. Just remember you two should be in different stages of your lives. If you can't seem to find ways to have fun together now and need the help of a internet message board, this relationship isn't long for this world.