Tell him that you won't be a part of this situation and that you won't visit his place. You can't force him to grow up, but you can remove yourself from a situation, you don't want to be in. If he wants to be with you, he can do so without having his mom up in your business.
So my bf is 28 years old his parents lost there house at the beginning of the year and they move in with my bf at his apt. 1 bedroom apt. I get along with his parents but he's a mommas boy I just recently found out that his parents sleep separate and he sleeps in the sofa but I notice his mom teats him like he is her husband she calls him to go sleep with her in the same bed? She gets jealous of me and she's always all up my business. What should I do? I been dating him for 2 years idk what to do