What do i do!

Nicole
My boyfriend doesn't have kids of his own but signed the birth certificate to his ex's kids. And now we are dating and I have my kids and he treats them so rudely but treats his (ex's) like angels . And I tried telling him multiple times to treat them equally as he would his own and he keeps saying "okay" but doesn't change. And I don't know what to do about his exs kids. Sure they are "his" they have his last name for he is on the birth certificate but I'm just wondering if that's ever going to change. Like what if me and him get married. He doesn't want me around them because his ex doesnt want us around.. like I totally don't get this.. I feel like since that's his ex he should let the kids go too. Or slowly drift away because they aren't his but still??