A.F.
Well, it sounds to me she has reason to be jealous. Must be her woman's intuition. Sounds like he's getting the best of both worlds, he's getting from you what he wants and getting from her what he wants. I would stop allowing him to kiss you and whatever else he does that you don't do with your other guy friends. If you stop doing those things he may be more vocal about his feelings for you. Maybe you can tell him that you have to stop doing that b/c you still have feelings for him and you don't want to get hurt. He might come out and tell you how he feels.
But while he is with her, I think you should stop doing those things, would you want him doing that with another woman if you were together? Later on if you are together you might think, well he did it with me, will he do that to me? Speaking from experience it can cause trust issues later down the road if you do start a relationship up with him again.
Good luck!