Heather - please do not take this as a 2 x 4 because it is an observation, not a criticism.
I see your life as propping up and taking responsibility for others. Trying to make things work for them and compensating for their deficiencies
And somehow you expected that they would do the same for you. Well people that can't even take responsibility for themselves are not going to take on other people (unless it suits them and their needs).
You said something revealing - that there was no-one 'there' for you. That is one of the lift dropping moments of MLC< especially if we do not have supportive family (or they are no longer with us)
Marriage can so easily slip from mutual support and help to a system of co-dependency where we prop each other up.
I think we know if we have been there.
This doesn't mean you have to become hard, but it does mean that you will need to adjust your expectations.
You have spent a long time in the university of hard knocks, and continue to try and shield others, probably because you didn't get that shielding yourself. Tough love, but actually being there for your daughter emotionally will stop the cycle.
You are not bailing on her, but trying to help her to grow up.
MLC is a kind of finishing school in emotional self sufficiency!