I'm with a vet who has combat PTSD... and he has never ever, not once, cheated on me. Not at his worst, not when he was triggered, and not when he has been drinking. He doesn't get on single sites, text other women or post pictures of his junk online. He has never forgot to not cheat, or had any kind of spell that turned off his moral compass. Even with PTSD and TBI from head injuries, he knows better, and he knows that his ass would bounce hitting the curb if he ever did. That is a no-go at this station... no second chances. If he cheats, HE messed up, and I don't care if he has a steel pipe protruding from the "no-cheating center" of his brain. If he wants other women he can be with them, but he won't have me.
It is a basic human respect thing.
PTSD is not an excuse to cheat, and not a free pass to stomp all over your boundaries, especially if you have already given him a second chance. It's also not an excuse to take it out on your kid. Don't buy into the poor self esteem manure they are shoveling at you.
I don't want to be one of those partners that lays down loads of rules and is constantly on his back.
You know what? There are times you just have to lay down the law. Setting boundaries and enforcing them is the only way that you as a supporter can keep from turning into a total doormat. You don't have to be on his back.... setting boundaries is all about what you can and cannot tolerate yourself. As in "I cannot tolerate cheating in any sense of the word, and I will not tolerate a partner that goes onto adult/singles sites. If you do so, I will leave. Period." Then if he does it, leave. You have to enforce your boundaries or they aren't real boundaries.
That isn't forcing him to do anything, that is telling him your limit. If he crosses it, then it is HIS fault. He is an adult. His brain isn't addled. He can comprehend the consequences of his actions.
But I'm not his punching bag and I don't deserve it
No you don't. That's why you have to set those boundaries if you want the relationship to work.
We as supporter give our loved ones with PTSD leeway in a lot of things, but it is 100% absolutely OK to have rock solid boundaries and deal breakers. It does not make you awful to leave him, even if he is sick. You aren't leaving him because he is sick, you are leaving him because he cannot respect your boundaries. You aren't going to make him sicker if you leave. His behavior and the consequence is shit he needs to own himself.
It is OK to not tolerate cheating, sneaking, or yelling at your child. And it is OK to be the big meanie bitch and stand up for yourself!