Am I wrong to be hurt by this?

TLDR: she told me the father is barely involved, but they talk twice a week. Is that inappropriate? I thought talking to an ex was on an as needed basis.

I’m (34m) in a relationship with a single mother (29f)who has full custody. She told me from the very beginning the father was barely involved and only saw his two children twice a month for two hours at a time. So we’re three months in and I find out they talk on the phone about twice a week as friends. I had no idea. She never told me they were close like that. I just thought once you broke up with someone and got in a relationship with a new person you were supposed to keep contact with an ex to an as needed basis. So I imagined she would be friendly while interacting involving their children, but not actually friends and talking just for fun. Am I wrong to feel hurt that she never told me how close they were?