How do I salvage my relationship...when he says one thing to me and acts another way?

I am so confused!! I have been in and out of a 4 year relationship where my boyfriend has been the sole "breaker-upper" everytime we have a disagreement. I have fallen in love with this man from the first time we were together, and from what he tells me his feelings are mutual if not stronger. Unfortunately, we have broken up and gotten back together so many times that this time he is ashamed to admit we are an item again. I guess my problem is that during numerous separations he had/has a married female friend that would always hook him up with her single girlfriends. These hook-ups led to him taking all of these women to bed. ually, he is the most compatible man I have ever been with, we may argue constantly, but our physical attraction and connection is unbelievable. He shares these feelings with me, and tells me he wants to marry, reverse his vasectomy,...etc..I have been very hurt by his total disregard for me by sharing intimacy with other women...but now that we are back together he is too ashamed to admit to this "match-maker friend" or any of his friends that we are together. He says one thing to me and another to them. How should I take this? He wants me to concentrate on "JUST US" and not worry about anyone else. What if he continues to go out with them, excluding me? Should I just suck it up and put all of my trust in him? He used to distrust me, now it is the total opposite. I feel like I am being used, but for what? If I don't call him when I say I do he gets enraged and threatens to break it off with me, or if I want to go out with my friends he freaks out! Am I being played? cheated on? Should I worry that he went from jealous and distrustful to all of a sudden this overly trusting man? Please help sorry for the lenghty ques.