My boyfriend and his ex wife

My boyfriend was married for 9 years. They have two kids under the age of 5. He’s been divorced for a little over a year. We’ve been dating 3 months. Ive met his family and friends, and he mentioned wanted me to meet his kids next. Is it strange to anyone else that he hasn’t told his ex about me? Or that he just told her a week ago that they would never be getting back together? He says the reason he wants to wait to tell her is because he’s afraid she’ll sue him for more child support or full custody. I don’t have kids so Idk what is normal in these situations. I’m trying to be understanding and not get upset but something just feels icky.