Can I also point out, at no point have you heard anything straight from the girlfriend's mouth? It's all rumor at this point. For all you know, someone told her that *you* threatened to stab *her*. Ever play telephone? If you really want a relationship with this guy, you can't let the rumor mill do your communicating for you.
That said, this doesn't sound healthy at all. Run. Run far, far away. Find someone to be with who doesn't play telephone, is honest, and who has a clear idea of what he wants. Your time is too valuable to waste it with juvenile drama.