Your best bet would be to back off. If either one contacts you then you can respond but don't initiate anything. Sounds like the relationship won't last and just be there for them once that happens.
Nah, sounds like a future marriage built to last to me!
The guy is obviously insecure, you should try to tell him that it's nothing more then texting and a frienship, over and over again until he believes it.
I wish you best of luck with this and I hope you can end up with both of them as friends!