Your husband is a love addict. I am going through something similar with my wife. I would suggest you read the book 'Lonely all the time' as it will give you a clearer understanding of what you are up against.

Get yourself in a position of strength in counseling so that you can give your husband a bottom line and stick to it. You cant force him into counseling but you can leave if he doesnt change. He is an addict and you will have to approach this as if he is an alcoholic, different drug, same problem.

He wont change unless he gets help and into a 12 step program for this. I wish you the best and take care of you now.