“I go to work and come home... If I am not with her she is constantly accusing me of cheating”.
Therein lies a lot of the stress for you, hon. YOU need a break. YOU need some away time. YOU need to go fishing, see a movie, walk around a mall, go to a baseball game.. something. You have to feel trapped and imprisoned.. and if so, you may start to suffer from depression. Yes.. take your grandson when you can but IMHO... whether she says you are cheating or not.. you have got to get some time away to relax, recharge and just plain think things out.
The first year of this I got a book on single parenting. I was basically a single parent considering the situation. I only read the first chapter. It was titled “Take Care of Yourself” and stated that you can’t take care of anyone else if you don’t take care of you!