How do you find peace in your heart when you resent having to financially support a father who was absent most of your life?

My father was never mean or abusive but never really matured enough to take an interest or provide for his three children. After our parents divorced when we were in our teens, my father rarely communicated with us. About five years ago my brother rescued him from living alone in a run-down apt in another city, and brought him to a subsidized apt in my brother's beautiful town. Now my dad is 90 and his small retirement does not cover his expenses. My older brother and I have to provide a lot of financial support to pay for his group home and personal expenses. I had long ago expected nothing from my dad but now it feels painful to give up my hard-earned money to a parent who did so little for me. Younger brother refuses to give him money or time. I love my dad because he gave me life, but I don't like him for who he became. Now he is bored and lonely and calls me every week to talk--which I graciously do. Older brother lives nearby my dad and takes on the vast majority of his extra needs--of which I am very grateful (because I wouldn't want to do it!). I visit four times a year to help out and send money monthly. My dad has no idea how we all feel, and is not capable of honest self-assessment. I would like to feel less resentful.