(((wife59)))
I am very sorry to hear about the pain that you're suffering in your marriage.

I can only imagine the devastation and powerful negative emotions that you're probably dealing with on a daily basis.
It sound as though your husband has a sexual addiction to me. Like every other addiction, there are groups that work through saying "no" and work towards obtaining and maintaining healthy habits. Like every other addiction out there, the one addicted needs to be the one desperate to overcome his or her damaging behavior. And, a lot of times, that equates to losing nearly everything that they have.
This is where it becomes personal. I cannot imagine ever accepting my bf's (or hub's) addiction to this dangerous and humilating behavior. My self-esteem sucks as it is...I just KNOW that I could not stand by and allow this to continue. I really advise you to go into therapy and work upon boosting your self-esteem. Pick up some new hobbies, unrelated to your husband ~ and become strong enough to step away from him.
You could write a letter ~ explaining that while you care about him deeply, you simply cannot accept his need to get physical satisfaction from other women. you need and deserve to be his one and only. If he is unable to live up to his commitment, then you need to step back and preserve your self-esteem. I might go one to say that if you saw him making a genuine effort to change his addictive behavior through therapy and support groups, that you might be willing to give the relationship another shot (in time). But you do deserve better than he's currently giving to the relationship. If he's unwilling to work on overcoming this addiction, than you're going to have to let go permanently. For your sake!
Gentle hugs and very best wishes to you!