How shall I respond to his ultimatum?

I am approaching 50 and have been separated from my husband for ten years, although we continue to live in the same house and are reasonably friendly. We have a 13-year-old son and my 89-year-old mother lives with us – she is in a wheelchair and housebound. Since I was 19, I have been in an on/off relationship with another man. He was married when we first became involved and, after seven years, I left him to marry my husband. When my marriage was at its worst, I rekindled this affair. He is now divorced and he wants us to get married and be a family together. However, my mother suffers from anxiety and does not want to move. I fear it would finish her off so I have asked him to wait until she dies. He has issued me with an ultimatum: either we live together now or we finish completely. When this man says that he wants you to be a family together, does that mean that he is prepared to help you look after your mother and be there for your son? I don’t think it’s kind or fair of him to give you an ultimatum. Of course, it can’t be easy for him that you are living in the same house as your ex, but I also understand that this could be too much of an upheaval for your mother. Explain to him gently that if you moved and she deteriorated as a result or died, you would feel responsible. Tell him that by giving you an ultimatum, he is making you unhappy and ask him if there is a compromise that you could make. Perhaps you could get carers in for part of the week to look after your mother, which would give you more time to spend with him. If he is worth having, he would be willing to be flexible.