I want Khula being the second wife

I’m a second wife of my husband when we got married, he told me that he has a wife with kids but she is separate and she is filing for divorce (which later on he mention that it was his guess that she was filling for divorce) I agreed to marry him because he told me that I will help him raise his kids as a good muslims.

since the first wife is a converted muslim. But now more then one year passed there is no divorce and he is telling me that for kids sake he has to go stay with her but he will not tell her ever and by hiding from her he will pay me visits. And he is also telling me if I give up my rights like about spending time, money, and other matter then he can manage the two wives it means he will come to me when he can and give me fix money but not equally. Bear in mind that our marriage is not disclosed to anyone in our families because he told me his case is pending in court about his children visitation and it can create problems for him. right now he has limited visitation to his kids due to his wife filed the case of neglecting( which is not true) and he talk to them over the phone,.

this is my second marriage too and I have one 10 year old and my husband passed away. By Allah’s guidance I’m learning deen and trying hard to practice in my daily life, Alhumdolliah. I have good heart and I want to stay with him and help him but no matter how hard I’m trying my mind is not in peace because I feel more like his girl friend, then his wife. I know he has his four marriages right from Allah and I have no objection but what I should do when I cant bear this. The way he comes and go its hurt me and my son need a father figure that’s why I got married which I think he is fail to be there for me and him he comes to me when he can and since he never want to tell her about us it will be difficult for him to do justice.

Please tell me if he cant do justice between two of us and I don’t want him to divorce her, can I ask for divorce? is this a sin? I’m mentally and emotionally getting hurt and it is also effecting my son. Please reply soon