My brother says he’s backing out of a deal we made. He now owes me thousands.

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Dear Pay Dirt,

My brother and I inherited our mother’s home, and my brother and his wife moved in. We had a gentleman’s agreement that at some undetermined future time when my brother moves out, we’d sell the house, the cost of any home improvements made by my brother would be divided by half, and my potential rental income would be halved, too and settled upon the home sale.

I brought this up again recently while paying half the property taxes again, and suddenly my brother says that this is nonsense and he expects to get half of whatever the home sale generates. He has already lived there for five years. Am I looking at lawyer time to fix this before losing tho