Loollipoplove, I understand why you feel let down by people you had relied on. It's horrible , but it happens.
You can't change others' feelings towards you except by changing your own behaviour towards them. Someone here wisely advised you talk about something else when you are with your friend. She has given you an ultimatum and I advise you to do as she asked. What she owes you is beside the point. Obviously she has done as much as she can. It's good that she explained this to you and I think she is worth making the effort for.
The loss of the company of your daughter and grandchildren is obviously very sad for you. Of course, anyone can understand and sympathise!
Again, it's really good that your daughter has explained how she is placed regarding her husband and fears of marriage break up. And it's good you understand her position. What you should do is agree with your daughter's decision, and tell her in a friendly way you will do as she asks with regard to meeting her and the children. She probably feels very bad about this too. All you have done for them is neither here not there in the face of your daughter's problems with her marriage.
Once you have come to the decision to do what your daughter and your friend ask you to do you will be able to stop obsessing and feel happier.
What gives you a warm feeling? 🥰