There is a feeling worse than unrequited love, and it's the sort of love that isn't unrequited, but intermittent.
Imagine loving someone with all of your heart, but they can only share their love back when they are not ravaged by depression and anxiety.
Now imagine that your self worth is driven by this fleeting love. It's painful, difficult and saddening.
Now imagine you have a few kids with this person, and they do the same thing with their own kids.
It is amazingly saddening, and I don't know how to describe this feeling other than heart breaking. And I wish I could change.