I don't know what state you live in, so the answers aren't clear. In my state (Colorado), there is no benefit to filing for legal separation. That being said, it's kind of like splitting hairs.
The others who have weighed in have certainly made great suggestions. My only suggestion is to change YOUR perspective on what this really means.
It sounds like your next move will be made out of fear that he's going to force you to do something you don't want to do. I understand that. But the forces of nature cannot be stopped, so the best thing you can do for yourself is to accept them and learn how to live within the framework of the change to get what you need from the outcome.
What I mean specifically is to put on a new set of glasses and see a separation agreement as a court binding set of rules for engagement. Use this to YOUR advantage too. I've been around here and in real life long enough to see spouses without one put the marital assets in jeopardy by assuming debt and ruining credit. If you have children, this is even more important - particularly if you've been a SAHM for any length of time.
You may also be able to stipulate that any of his income that's used to pay for OW must be documented and come off his side of the ledger in the event you D. You don't want him buying her a car with money that is legally yours, right? Not saying your H will, but they do lots of insane things when they think they are off the hook financially.
You also legally document child support and banking arrangements before he decides he doesn't want to pay you anymore without you agreeing to that.
I'd run - not walk - towards the nearest mediator to get this hashed out. Mediators cost at least half the $$ to use instead of a lawyer, and if you find the right one, they are fair. I found one here in Denver that has lots of experience in family court, and both my XH and I liked dealing with him (though it was emotionally difficult too).
And I'll weigh in with the rest of the good folks here who said that you should beware of the trap of MC for a year. I also fell prey to the belief that he would come to his senses and therapy would help. But my XH didn't not want help. He wanted to be left alone. He didn't do the exercises, and after 3 months, he quit going. And yes, he used the experience to say quite loudly, "I did everything you requested and it just didn't work for me."
Don't waste your money. If you want to see an IC, go for it. I'd recommend it anyway. But leave him out of the C trap. You might be really sorry to hear what he says down the road.
I was separated for 2 years, and the initial separation agreement took away a lot of the underlying fear I felt about the eventual divorce. I'm not saying it's a magic bullet or anything, but at least if you have a legal document stating what is and isn't permitted might help your cause down the road more than marriage counseling for both of you.
Good luck!
Betsey
"There are only 2 ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."
