Oh Penpun This situation is devastating, demeaning to your natural humanity, and so emotionally damaging on all levels. It's unfair and leans into you being a trauma victim. And that will need long term care.
All of this coming from the kindness and compassion you offered to him. And that point is one that I want to say is who you are which is being eroded and broken right now. It is so understandable to question taking him in. Which must be such an emotional dissoance for you.
You have shared so well. Shared the vulerable state you face which is true courage to do that. This burden you carry deserves to shared. To allow others to hear you see you listen to so it does not become a festering sore eating at you now and into the future. The words we say out loud & share takes the jagged shards of our feelings and offers a narrative for us to see and others to see. It helps us to see better but you seem to see it all to well. Yet sharing is a step forward. There may not be solutions right now but there is support, understanding and compassion here for you.
If you can be kind to yourself. Give yourself grace. That compassion you offered your dad may seem broken but it is there give it to yourself. Allow you to feel it for you.
Keep sharing here we will be here for you