Baby mama drama or is that what he wants me to think

I’ve been with my boyfriend for 2 1/2 years. He has three children with his ex girlfriend ages 8 and 6 (twins). He moved into my apartment after our first year together but he doesn’t bring the kids over to the house. I have told him many times that I don’t mind if he brings them over and that I could even help him with doing homework and feeding the kids dinner so he wouldn’t have so much to do on his own on school nights. But he still takes the kids to his mom or grandmother’s house on school night even though he saying that it feels like they are unwanted there. He told me that he and his ex do not get along but he invites her to all of his family functions which I have to find out from other people. This bothers me because he doesn’t even invite me to his family functions. I told him that not being invited to his family functions bothered me and he said that it wasn’t done on purpose and that it never even crossed his mind. I have seen his kids 5 times in the past 2 1/2 years. Am I overreacting or does this situation sound off? Why doesn’t he want me around his kids? Why am I not invited to his family functions? Why isn’t he being honest with me about his relationship with his ex?