What to do in this situation?

ok, so i am in a relationship with this amazing guy. he is my freakin' dream guy, he's handsome, smart, caring, considerate, generous, he has a good sense of humor, and he's mature. but then, this girl comes along (i'm bi, so NO rude homophobic answers please) and she is all the same as he is, only she's a giel. ah! i like them both very much, but what do i do?!