First of all, welcome to the forum!
Second, oh lordy lordy lordy. Yet another case of let's-have-a-threesome-and-invite-the-person-to-move-in-with-us.
SLOW THE FCUK DOWN!
Actually, I'm not going into this because I'm sure other people will and it's not my life so I don't really care what you do. I'm convinced that this is something people have to learn for themselves the hard way.