Boyfriend super close with ex girlfriend

My boyfriend and I have been together almost 2 years and we live together. He is super close with an ex girlfriend that he used to sleep with. She makes me nervous because she has cheated on her husband who she has 2 kids with. They talk everyday and text everyday. I don't like her and don't want him talking to her. He says they are just friends and I am ridiculous. I don't think its too much to ask since they used to sleep together.