The first thing to do is breathe! I know that you are scared, but you are stronger than you think.
Sounds like your may be depressed and while in depression they aren't attracted to us because they've lost that loving feeling towards us and yes, most likely he's still in contact w/the ow. It could be emotional or physical, but he's still thinking about her.
Are you the one that pushed for counseling? As long as the third party is in the picture, counseling most likely won't work. Sure, he goes to the sessions, but is he really listening, talking and doing what the counselor has suggested or is he just going through the motions? Are you in individual counseling? If not, that may be a better choice for you at the moment since it doesn't appear the joint counseling is helping. You need a safe place to go in order to talk more openly about what your feelings, i.e., just as he needs to do the same...but he will need to make the decision to see professional help when he's ready.
As for sex...have you been to see your physician to get checked out? If he's been visiting elsewhere, you do not know what he may have picked up and brought home to you. Get yourself checked out and take measures to protect yourself even if he says he doesn't have anything. As long as he's out there, you don't know if he's using the proper protection or not.
So, tell me...what happened about 12-18 months ago? Did something change w/your h? Did he get promoted, lose his job, have a health crisis or did someone close to him die?
You asked a question on a thread that I created concerning the distance/pursuer. How do you stop your pursuing? It's not easy, but you can do it. When the distancer senses the pursuer is not reacting a certain way or as they say, takes the distancer's bait, the distancer will try various things to bait you, the pursuer to get you back into the game. If you can find a way to not react to what he says or does, this will be the first step. You have to find a way to stay the course. The less you pursue, the more likely your distancer will become curious and start pursuing you....but you can't let your guard down. As they say...don't snap up the bait. Continue to remain calm and just go about your business. Sometimes they are nasty to get your reaction and then there are other times, that they will play nice...but it's all the same...to get your attention and yes, to see if you are still there waiting on them.
Go back and re-read the first page. I identified some things that you shouldn't be doing. Maybe you will find something that you can stop all together or gradually, but you need to start thinking about you and your son right now.
Amy, you can't control him or tell him how to feel. You didn't break him, therefore you can't fix him. You can only control yourself, how you feel and how you react to him, his comments and/or behavior. BTW, you will need to drop your expectations of what you think he should be doing down to 1, if not zero.
