I’m so sorry you’ve had such a terrible time. It seems from your post that your daughter has rather taken you for granted while she’s been going through changes in her life and you’ve done a great deal to support her, putting your own emotions to the side.
You’re absolutely right to insist that your grandson goes to live with his mother. It’s not clear why your daughter wants him to stay with you. However, he’s not your responsibility and in any case, the family should be together.
Keep quietly insisting that he can’t stay with you as you need time to yourself now. Your daughter may not like it but she’ll have to accept it. Tell her you don’t want to fall out with her but that time to yourself is urgently needed. Most women who have lost their husband or partner take a while to grieve, going through all the emotions of anger, hurt and so on. You’ve not been able to do this but you can’t keep putting it off or your mental health will suffer.
Is there anyone else in the family who could speak to her? Also, I think you should explain all this to your grandson so that he understands that you need to be on your own for a while.
It might be helpful to you to look on the Cruse Bereavement website www.cruse.org.uk. They have very good information about the grieving process and you could show this to your daughter to explain in more detail how you feel. It’s easy for young people to think that an older person will quickly get over the loss of a spouse and your daughter might need to know that’s far from true.
I hope that you can reach an understanding.