Your bloke sounds extremely selfish - and anyway, why did you have to go with him to stay overnight, it was his appointment?
BTW you don't have to give back the engagement ring - it was his gift to you. It's absolutely no business of his brother's.
You won't be alone for ever, this is just a bad bad time for you. He's very selfish not to let you mourn your gran.
Do you have anything in writing about the money he owes you? Don't do anything illegal, that would be stupid and in the end, would make you feel even worse, it's just vindictive.