Kand, your H needs to end contact with her via a no contact letter that is written together and mailed by you. It is very much in your H's hand to end contact, he just doesn't want to. If he stopped taking her calls, she would stop eventually. sample no contact letter below.
If contact does not end, then you need to call her parents, husband, etc and expose the affair.
Secondly, what appeals to your H about women with emotional problems is the ability to solve problems and be the knight in shining armour. There are many other ways to meet that need of us, such as appealing to him for his help and assistance in your life. My H has this need and I fulfill it by asking his opinion often and asking for his help in fixing, repairing things. This makes my H feel needed. And that is what your H wants, he wants to feel needed and looked up to. You just have to find the way to help him feel that way by trying different things.
A good start would be to read the books, His Needs, Her Needs, and Surviving an Affair. There are some very good questionaires on this site that will help you better understand and meet your H's needs.
Dr. Harley?s (From SAA)
(OP), I want you to know that out of respect and love for my wife and children, I have come to realize that I must never see or talk with you again. My relationship with you was a cruel indulgence that (BS) did not deserve. While I cannot completely repay (BS) for the pain I have caused her, I will do my best to become the husband she?s been missing. I care a great deal for my family and I would not want to do anything to risk their happiness. I will not make any further contact with you and I do not want you to make any contact with me. Please respect my desire to end our relationship.
Sincerely,
(WS)