asked him for input - he shrugs and says I don't know - you figure it out. So, in some ways, it does make me bitter.
This sounds like an old pattern. Why does he abdicate responsibility? Probably because of some stuff about him and some stuff about you. Why do you let it go and bitterly go on to fix things yourself? Probably because of some stuff about him and some stuff about you.
What can you do to break the pattern? Quit playing the same role.
Quit being his mom. Treat him as an equal partner who needs to own his responsibilities. Time for him to step up to the plate and time for you to share it.