Help? Advice? Pleasee

So My On and Off Boyfriend Of 1 year has two Daughters (2yrs old and 3yrs old) they have different mothers. And I didnt find out about one of the kids till two months after we were dating. I dont have a problem with kids at all. He doesnt even bring them around. Its just that he doesnt see his kids as often as I would want for him to see His kids. I encourage him to do so because I grew up without Ny Biological Father. Its Not only that, I dont know if im being selfish but Im tired of hearing of his baby mothers. I get it, one kid but then to have another kid right after with a different woman?

It kinda makes me mad. I always thought I would be with someone who doesnt have kids like me and that we would both be new to experience parenthood. What should i say or do in a way that wont be mean or rude to him???