How do you save your marriage after a long-time emotional affair?

My husband and I have been married less than 2 yrs. We have a 3 yr old child together. My hubby also has a 14 yr old son with his ex-wife. In the past, I have intercepted text messages from the ex-wife to my hubby that are very inappropriate, ie. I love you and I think of you, I miss you, I wish you weren't with her, etc. My husband has admitted to having an inappropriate relationship with her and says that he knows it would never work between them, but he still loves her. He knows that she manipulates him and uses him as an ego boost. He has also admitted to me that she does alot of the things she does to anger me. She left him over 10 years ago after cheating on him with a man that was nearly 40 years her senior. There has been a general deterioration in our marriage due to the infiltration of the ex-wife and also due to the fact that he allows her to do these things and won't put a stop to it. I know I am up against a great evil, and I know that it will be extremely hard to overcome this. A few months ago, my husband moved 8 hours away to undertake a new carrer opportunity. A few weeks after he left, he told me he wanted to separate. Then I found out from his ex-wife that he enlisted her help in finding a divorce attorney. Last week, my hubby tells me he has had a change of heart and that he wants to work on saving this marriage and all that jazz. Well, I made the 8 hour trip to where he is living, and when I got here I found over 100 text messages between my hubby and the ex, professing their undying love for one another. She recently broke up with her fiance and so she was in need of an ego-boost from my husband. I confronted him, he says it is over between them, and that he wants me and not her. I am not even sure that I can learn to accept this, or figure out how to trust him! I don't want to be the nagging wife, or the nosey, snooping wife. Is there anything I can do to encourage him to be a stronger husband with a deeper sense of respect and commitment to out child and our marriage, or am I a fool to believe he can let go of what he used to have? I do not want to get a divorce, I believe strongly in the vows of marriage, but I do also believe that this is considered adultery.