have a g/f but there is another girl i like
I agree with Diana, crushes are actually kind of normal when you are in a relationship, but once you take the next step your current relationship is over.
Think about why you live with your gf-you probably love her. Something about her made her attractive to you, if you can't remember what that is, try to turn up the chemistry and establish the relationship you have with the "other" girl with your current girl.
Dating the "other" girl, aka your girlfriends friend is a VERY bad idea.
2014 SR 3sGT
2015 DCB CX5GT