What should I do because I'm really interested in her.?

Well I just dumped this one girl who really didn't care about me at all (I really don't want to talk to her ever again). And well there is a girl now (lets call her Steph) and Steph has a lot of things in common with me from the genre of music that we listen to, we both play guitar, both of us are involved in a sport, and we are both in our high schools musical; and we're both huge Jim Carey fans; and we both love SNL. Now Steph is a freshmen and I'm a junior and I have no clue to how interested she is in me but I will just go with it (what do I have to lose). I'm definitely wanting to wait a month before I jump into another relationship. But new problem a "friend"/teammate (swimming team) of mine is going after Steph as well but he is a senior and I know for sure that he has smoked weed and still does to this day because he has told me. So I don't want to be mean to him because he is kind of lonely and he really is lonely. And people have been telling me to just go for it but I really didn't want to be mean. And I need to wait a while before I jump into a relationship again. So what am I to do? And I don't want to feel guilty about any of it afterwards. Your opinions.