I don't want to sound like a 'lecturer' or a Barbara De Angelis here..lol..however..

My first instinct is to say 'what's up woman???' as in how can you be with this man? But of course there is reality to think about, women ( I was with a similar man for years because of responsibilities like a child etc and women would say the same thing to me 'what's up?") do stay longer for reasons that vary.

Yes I can say this is a situation where he is being dominant and your being subservient, but it's not something that is close to the concept of a healthy d/s relationship. He is not respecting you as your respecting him, and in your heart of hearts you know this yet you are going through the motions as you don't want to sink to his previous level and have affairs, which is noble and perhaps is right - as you understand where your limits are. However he is with you, your working your butt off, and he is having online affairs at the same time.
An affair is an affair, regardless of whether he is physically feeling up the other women, or cybering with them, what makes it an affair is that he is emotionally unavailable to you.
I agree with the counselling option, it's worth a try as you value the institution of marriage, but he is also utilising his illness as a bargaining tool to control you, yet he is capable of experiencing sexual arousal online, or by you giving him oral sex etc.

I sincerely wish you all the best, because reading what you wrote really touched a chord within me. I was in a similar situation a few years ago, I tried many things, made many efforts yet the other person's behaviour didn't change, or it would change temporarily only for it to revert to the same thing. It wasn't so much the 'affair' aspect (I was walking a thin line and considered those options but knew it wasn't in my nature to cheat) but the complete disrespect together with excessive gambling, me being the provider, parent, lover, 'wife', cleaner..while he would blow a week's earnings and I had to borrow money to buy food.
There will come a point where enough is enough, and if this man doesn't make any effort to change even after you try counselling you will know.

For me it was a fluke comment an acquaintence made to me - as they say strangers see things from another vantagepoint- and their comment or question that made me wake up was the following:
'Do you see yourself living out the rest of your lifetime like this?'.

the concept scared the crap out of me..

and I just made a decision straight away..