baby momma drama

I am so fed up with my OH never standing up for himself. I love him and his little one so much but the stress is driving me insane. When we first got together she made up their child was in hospital when she knew we were going on nights out but wouldn't let him know what hospital or go then she started saying that their son was asking if his daddy loved her (he was 7 months at this time) then when we decided moving in together she went crazy at him telling him that we were obviously trying to have a baby etc and he had to tell her everything now she's got a new man moved him in after 1 month and my OH says he wants to know who's living with his son because she barely knows him yet he won't ask her. I don't see how it's fair that she has a say in everything my OH does because they have a child together but because she's his mother he shouldn't be questioning her. He's not allowed on the birth certificate and she's told him that he shouldn't be having anymore babies because their so would feel out of place. We had started ttc 6 months ago and I think I should put it on hold for the fact I don't want his son to be taking out of our lives, it's not his fault he didn't ask for all this. I really don't know what to do, she rings and texts everyday having a go, we aren't allowed to take him on holiday but her and her new man are, we have to let her know everywhere we are going and what he eats. I'm getting fed up with it, it's always drama upon drama. How do I approach this or any advice on how to sort ot