Just to be clear Padraic is a simple man but he knows Colm better than any living person. He sees exactly where his friend is headed and wouldn't give up on him no matter how stupid, stubborn or pathetic he appeared to everyone.

Colm wasn't tired of his friend. He wasn't seriously that interested in legacy all of a sudden. He was suicidal. The old woman that everyone avoids probably represents death so everyone sorta knew it was coming but avert their eyes and pretended to not see her.

It was going to be someone and Padraic wasn't going to do nothing and let it be his best friend. He did finally give up at the end. Burning Colm's house wasn't revenge though, not really. More like doing it himself so his friend doesn't have to hurt himself more before finally ending it.

It was only then that Colm realized that his friend needed him and chose to live.