I had a great talk with a woman today who is going through a similar sitch - and she put her foot down early on. She told her H that he has to do fifty percent of the changes or the marriage is over.
Hope,
You are responsible for your 50% of the MR and your H the other 50%. You need to give 100% to your efforts to effect change in yourself (i.e. your 50% of the MR)in order to hopefully sway your H to want to make positive changes of his own (i.e his 50% of the MR).
From your description of things your H is acting like a complete a$$. He needs to understand that when it comes to sharing your S5, he needs to be an adult and be fair and reasonable. Dia is right- this behavior of his could adversely affect the amount of custody he is awarded in regards to S5 in the future.
Is there anyone in your extended family that could have a frank conversation with your H about your sitch- preferably male- someone who might have a chance of setting him straight? What about your MIL?
You need to continue working on not putting up with your H's crap anymore. I still haven't finished "Love Must Be Tough" by James Dobson- I've been too busy with work and my own damn D- but I've liked what I've read thus far. I recommend you pick up a copy for yourself.
As far as the agreement to go to MC, this is shaping up to be just what it sounded like when you first mentioned it- a ploy by your H to get what he wants. I agree with what someone else above said about your H- he is acting like a bully. The only way you are going to impress upon your H that you are serious is by playing hardball of your own. In light of recent events, I'd consult with your L regarding your next step.
Hang in there.
M: 41 W: 39 S: 11 S: 10 D: 4 1st contact w/OM: 1/19/09 EA began: 2/14/09 EA discovered: 3/1/09 I file for D 8/25/09 to protect myself _______________________________