I agree with the post that says a letter should be written to OW ending the relationship. You should read it and mail it together. I know it is hard..You don't want to rock the boat.
A mourning process also occurs when WAS leaves OW. But by keeping contact only prolongs that process. Maybe you could go to counseling together or seperately to deal with this?
Your H wanting to renew your vows is great. However, his actions are conflicting because he won't stop the contact with OW.
I highly recommend a book called Love is Tough by Dr. Dobson. He states that as long as you are putting up with Ow it is like having a third person in your bed. Lovingly detach. He also was the one who recommends writing the goodbye letter to the OW.
Baby steps right now. But set some sort of boundaries. Your H will respect you in the long run. I promise.