You have been responded to by a non-professional, who may have given you the answer you needed. Let me know if you would still like my input as a doc. I ask this because there is lots to do, and answers take time and effort.
Well I don't blame you for having trust issues. It's not like this was a one time thing. It's not even one woman, it's many. He even left you for them. I'm not sure if you will ever trust him given what he has done in the past. My fiance cheated on me with a woman for 2 years and even though it's one woman and it's been over for almost a year now, I still have no trust. If he had cheated on me several times and left me each time then I don't think I would have the strength to continue on in a relationship like that. The hurt and betrayal I felt for his affair has left me scarred and has damaged our relationship almost to no repair. We have gone to counseling to work on our issues and are doing better now but the mistrust is still there and the worry that he will do this again some time down the line. Well let's just say he better be good at hiding it because if I find out, it's over for good. You have to demand respect in your relationship and the fact that you allowed him back in your life numerous times after he had done the worst to you, shows him that you will accept the worst from him. He has no consequences to his actions. Why wouldn't he continue to stray when you have let him back into your life over and over again? He knows he can get away with it. Have you tried couples counseling? I don't think he will change much and it's up to you to decide if his infidelity is something you are willing to put up with. If it is, then you just have to deal with it, if it isn't then you need to think long and hard about whether this is the type of relationship you really want to be in. This is just my 2 cents....I'm not the expert in this forum so you can take my advice with a grain of salt. Good luck hon, recovering from infidelity is the toughest road I ever had to travel so I can only imagine how you must feel.