Confused

Am a mother of three and separated. I met someone 2 years ago and we are still together been living together for a year now. He has a girlfriend back in his native country. He also has a son from an ex girlfriend. When we met he went back home and said he would end it as he had just been introduced to her. I was to later find out more happened on the trip. I put up a picture of us up and she sent me quite the nasty message to which I did not respond. He later went and keeps saying he doesn't meet her but photos always show up. They both can only have children through IVF and he feels that he should help her out and I totally understand that. What I have a problem with is him saying that he wants to help her be a mother. He argues that if he tells her outright that he just wants to have a child with her but not marry her then she will decline. I tried IVF and it unfortunately failed. He keeps in touch with her and so does his mother who though polite and doesn't say so would love for him to marry her. She asks some very interesting questions like how is the father of your children doing? The age difference between my youngest and his son is soo big? What will I do when he brings her over? Her and the girl are namesakes..... I feel soo confused.