I think the fact that you haven't seen him in four months could be very relevant. You and he are in a relationship, to be sure, but if it is long-distance then for one or other or even both of you, such a long time apart could lead to the relationship being less "real" than it was when you first got together. Perhaps that is why he was seeing this other woman, even if it never went far, and been coy about other female friends he may or may not have been spending time with. Then again perhaps he has been innocently seeing them and feels unfairly accused of fooling around.
At any rate if the trust between you is breaking down, and it certainly seemed to be, that ought to be addressed and fast. How you should go about this I don't know, but probably the best thing to do at first is, rather than confront the issue directly -- things could easily get messy especially if accusations get thrown around -- to try to arrange to meet up soon. It would be a good chance for both of you to remind each other that your relationship is real, to bring it back to the fore. Obviously don't avoid the issue forever but the first thing to do I think is just to ensure you spend quality time together, and only after that can you tell if you want to confront this breakdown of trust more directly or not -- but leave that until afterwards. The next day, in a comfortable situation such as a private lunch or over a movie, and bring the subject up delicately.
From the sounds of things he might even be slightly worried that you are going to be jealous and is being evasive on the issue of meeting other women. I'd try and find out why he is being so evasive, and not assume that he's messing around behind your back to start with at least. If he is of course then you probably should cut him loose, but on your account it's not clear that he has been and indeed the first time it turned out to be false rumours. I wonder how that impacted on him and you both.
I hope this advice is useful, I don't know if it's any good though.