Boy, I really sympathize with you. Firstly, you cannot "convince" your H of anything. He has to reach his own conclusions. I'm sorry if that's not what you want to hear. There is no magic formula, what works for one couple may in fact backfire for another. And why would you want to try and convince him anyway? Wouldn't it be more desirable and honest if he came to that conclusion on his own? There's no way I would want a man with me if he feels he's being "forced" into it.
Please stop pursuing him. You are only pushing him away further. Stop it. Immediately. As hard it is, try your best to ignore the OW's presence. She is not the reason your M is in trouble. She may add to the confusion right now, but the problems were there before she came into the picture.
You need to figure out what those problems were. Don't do this by asking your H. Back off from him. Make a list of what the problems were. Post them here if you want - others can help come up with creative ideas and solutions.
GAL - do you work? If not, is that something you could do? How old are the kids? I know that I'm going thru something similar, my kids are 7, 3 and 18 mos - I don't like the idea of them being in daycare, yet I think on a part-time basis it would actually be more beneficial to them than being trapped in the house all day with their crazy momma! LOL
You need to get back your self-confidence and self-esteem. They will go a long way in helping you get stronger and able to deal with things better. Re-invent yourself. Do what YOU need to do to make yourself happy. As you find yourself getting strength and getting more comfortable with a "new" YOU, your H may come back around. But until HE decides that's what he wants, work on YOU.
Here's a trick I've been using lately to help me improve my mood. I think of my SO as someone I want to date. I've listed the things about him that I like. I think back to the early days when things were fun, carefree, lighthearted. I do whatever I can to maintain that air of easygoing"ness" (LOL- new word) and happy fun times. When he says something that perhaps I don't agree with, I think about something from the past that he has said that's made me happy - I swear, I've smiled at him when he's said something that I think he's saying just to get me going. When I smile at him - it probably completely throws HIM off track. LOL I ignore our history (the bad parts) and focus on the positive. If anything, it makes them curious.