He has four kids

I'm pregnant by a guy with four kids. 2 (age4&2) is his and the other is his step kids(8&9) that he's raised since they were babies. He's never been married. We been together for 2 years and we love each other. I adore kids and hate that he doesnt bring them around or even know who i am. I met them twice and the first time he had me stop calling him babe in front of them. He says it's up to their mother but I'm sure she hates me. I understand women don't want their kids around their baby father's gf but I really want the kids to be apart of the new babies life. Also she had a bf living with her and the kids for a while now. And his oldest son had to tell him. I don't get it. I'm not a bad person. Should I just drop it?