Infidelity Support Group
Any relationship in which one partner engages willfully in sexual relations with another outside of the partnership is considered to have experienced infidelity. This breach of trust is often traumatizing for the faithful partner as well as the relationship, and support is often needed to heal emotionally and to decide whether or not the relationship should continue after...
Here's what you do. Ask him to have the password to his Facebook account, if you don't already have it, so you can read his interactions. Ask him if he's willing to show you his text with the woman in question, without needing to "clean up" anything. If he won't grant you access to view them on the spot, and give you his user name and password, he is hiding something, and that is always bad.
Then let him know what he is doing is forcing a decision. He'll either cut off all contact with her or with you. Which will it be? He will have limited time to decide.
After that, start following the "180." You can find the details here:
http://www.dailystrength.org/groups/healing-infidelity-through-faith/news/view/3932216
I'd say work it strictly. The idea there is both to prepare you for independence if and when it comes time for you to give up on him, and let him know you are serious and this is an issue that is "life and death" to your marriage. He'll either pick you or he won't.
Keep in mind, during an emotional affair as he is having (anytime someone spends more time communicating with a woman other than his wife is an "emotional affair"), he has justified and rationalized his actions. He probably really does believe this is all innocent and no big deal. He probably things he wouldn't cheat on you, even though he is having an emotional affair with her right now, simply by texting and talking with her a lot, even if all they ever talk about is the weather. If he is spending more time with her than you, communicating more with her than you, his priority is mixed up and he is way too attached to her.
Until you can get him to realize that, he's in danger, and your marriage is in danger, as you've already felt.
the fact he is against therapy because of a childhood experience? he needs to grow the heck up. he needs to be more concerned with his marriage. the fact he says he wont cut the friendship? sounds like that relationship is more important right now. (these WILL escalate).
i would do what cole said and work the 180.