My girlfriend used to pull shit like that and hang out with guys she had screwed around with in the past, and I never complained, but it did bug me. So back off. Regardless of what she tells her boyfriend, he still won't trust you unless you're a buddy of his. Whether or not you have romantic feelings for her anymore is trivial because no matter what you say he will think you do because you did in the past. Plus, the fact that the two of you are trying to spend as much time together as you possibly can, even if its a few days a month because of your busy schedules, is definitely enough to raise suspicion. I'm not saying to end your friendship, but let her make the decision as to how your friendship continues from here. If she loves her boyfriend and knows this is really upsetting him, she may back off. And if she does, don't push her.