If I were you I'd break the problem down into lots of smaller ones something along the lines of this if at all possible.
1. Try and get some regular assistance with your kids aprticularly your oldest daughter. Some respite care even if only for a few hours either from an agency or friends and family will help give you time for yourself.
2.Consider carefully whether jealousy motivates you. You seem very wrapped up in the idea that you don't want anyone else to "have him". If he's not for you, then fair enough, but it's not appropriate for you to worry after what he's doing if you split up.
3. The women he slept with are of no bearing on your future, you must disregard that if you are to have one together or apart.Hanging onto past hurts and slights will only drag you down.
4.Is there any way he'll really talk to you? Often we men show our emotions either badly or not at all, but it doesn't mean we don't have them. Anger is often the only emotion some men feel comfortable showing no matter what they might be feeling, so if there's any way at all to get him to communicate, please try and use it.
5. If you want out, then treat him like you would a drug addiction. Avoid him like the plague, fill your days with positive steps towards your future and work towards goals.
6. Remeber you are entitled to be happy. It wouldn't put me off a woman just because she had a disabled child (I have a son whose deaf and another whose ASD), most men are not as shallow as you'd suppose, so after a period alone, learning who YOU are again, of course there is someone out there for you.
7. You have a future, you just need to choose what it is and act slowly and calmly towards it, without jealousy or resentment.Don't use your valuable energy on anything negative.
I'm sorry you are having such a hard time,pretty much every situation where people are unhappy can be improved upon, you just need to make the decisions to make it happen and