I am wondering - is he living with his other girlfriend now How is she feeling about all this anyway? I think at the very least in your position I'd try to open a dialogue with her before moving, if she hates you or is excited to meet you, well that's info I'd want to know before showing up. I'd want to know if he'd actually kept her informed or if he'd minimized your existence to her too.
Either way I wish you luck.
Happiness will never come to those who fail to appreciate what they already have.