Ex-Girlfriend

So my boyfriend's mom still hangs out with one of his ex girlfriend and he failed to tell me bout her being at his mom's house til 3 days later. He told me he was going to stay at his mom's house for an hour and half to hang with his mom. I dont understand why his mom is still hanging out with his ex. He is always at work or at home with our children or me, I know he isn't cheating but I think it's very disrespectful on my end. He wants to build a future with me, but I dont want to build a future if I'm going to be subjected to have run ins at his mom's house with his ex-girlfriend. Also I don't get along with his mom she bashes me as a person and a mother, she has told me all I'm good for is sex and food. I'm madly in love with him but I dont know what else to do. I have told him how I feel andbhe said he has told his mom to stop talking down to me but she is her own person. He doesn't want me to leave but I can't/wont deal with his mom poking her nose in our business or bashing me. What should I do?