Relationship advice requested

Hi everyone! This is my first post! I'm in a relationship and I'm confused about what the best thing is to do. I love my boyfriend. I love his two kids (8 and 10) that mostly live with us. This has been my only relationship. We've dated for over four years and I'm getting tired of waiting for marriage. It makes me feel like I'm not good enough. It seems like his oldest son will hate me forever no matter how hard I try and his ex-wife is constantly trying to drag me into court and disrupt my life. I still love him and his children. I have told him that I want children of my own and I want to get married. He wants to start having children in the near future but he still refuses to tell me why he doesn't want to marry me. He is in his 50s so time to start a family of my own with him is running out. I'm so confused as to why he doesn't want to get married and it makes me feel so insecure. This has taken all the fun out of the idea of marriage. Has anyone been in a similar situation? I don't want to be wasting my time but I love this family.