Unfortunately for you, beauty isn't everything. This girl sounds like a player, and though it is fine to have a crush on people like that, you went much farther than a crush. In addition, this girl also has a boyfriend. You mentioned that you didn't talk very much, you just kissed a lot. If you truly like this girl, you should actually try and get to know her instead of just making out for 3 hours. On the other hand, if you are one of those people who just wants to get physically close to a girl without having any reall relationship, by all means proceed