Sounds like you two are sisters by different mothers.......
B,
You owe him nothing. You did what you needed to do by taking care of your parents to the best of your ability. I would give him a time frame as addicts work on their own clocks and this could take him years to move out.
I would not subsidize him in the least. Help him get settled and move on in life. You has taken up enough space in your brain for a life time. Walk away my friend you are entitled!! Hugs!! (you might consider seeking out a therapist or some alanon meetings so you can make peace with this yourself)