Boyfriend still hangs out with baby mama

I've been seeing this guy a little over a month and he has 3 kids from a previous relationship. He told me they still have family days because they said if they ever divorced they wanted the kids to see they are still a family no matter what and have a healthy co-parenting relationship so every 2 weeks they get together and take the kids to the aquarium, or park, or movies or out to eat etc. This weekend he and her are taking the kids to the zoo. His baby mama said I'm welcomed to come if I would like. I have no issue with his baby mama, plus she's dating a women rn.... But I am extremely insecure. I'm not gonna deny that. And my last relationship my ex was a serial cheater. He had a lot of severe mental health problems so his serial cheating wasn't even the biggest problem and he was low key abusive. I know I've only been with him a month and stuff but I can't help but feel jealous and insecure.