I'm reading through this and so far I'm getting
He said I undermined him to child.
I said he undermined me to child.
He farted for 5 seconds and took a piss with the door open and said " I can do what I want in my own home"
Was the "undermining" you him belching/ farting or something like that and the " undermining" him you asking him not to?
This makes no sense at all. None whatsoever.
It sounds like he has dreadful manners inside the home and has ramped it up a fair bit in response to the criticism.
You view the ramping up as bullying, chances are he views the criticism as bullying.
It is all fine and well people saying if someone does something that bothers you if they love you and respect you they would stop doing it. But often the thing that is bothering us may be something we have no right to let bother us (couldn't think of a better word than right) and by our inability to control our feelings about the matter is the thing that's the real problem.
You say you cannot leave him, fine that is your choice so if you are going to stick around for the next potentially 40+ years despite thinking he is a gross pig how are you going to deal with that? Are you able to take a step back and look at the situation and asses if you are playing a role in the behaviour or not? Are you willing to come up with some stratigies in order to manage your response to it?
Because that's what sticking around in a relationship that has clearly run its course means. Unless of course you fancy spending the next few decades with you both slowly simmering in resentment and hatred until you both cannot see the wood for the trees and the impact it will have on your child.