I agree with Marcus and BG - you have done everything that you are "supposed" to do. If HE decides to fall for a mono-girl...HIS choice. If HE decides to end his other relationships to pursue a monoship with her...HIS choice. These are not things that you can control.
YOU get to decide if being with someone who is -
constantly finding and meeting new girls
...never know what things are going to turn into, or if I should expect a phone call saying he just slept with someone new or if he's in love again.
is the right relationship for you.
I don't know that it is a requirement that she want to have "anything to do" with you or his other girlfriend. That is something that SHE gets to decide.
If you are convinced that he has been absolutely upfront about your existence (which would be an absolute requirement of mine - for me this would require at least one confirmation phone-call or e-mail) then I would say that it is out of your hands. She can contact you if she needs to. You can request that he not talk about her during your limited time together/ short phone calls - that is between the two of you.
If she wants to keep her relationship with him separate, and he agrees to that - then my suggestion would be to focus on YOUR relationship with HIM and only inquire about HIS relationship with HER as it affects you DIRECTLY (i.e. scheduling of your monthly get-togethers, 4x/week phone calls, safer sex issues, etc.)