He suddenly and inexplicably ends a years-long friendship, is willing to mutilate himself for extremely petty reasons, is very slow to react to Padraic setting his house on fire, and mentions he struggles with "despair" in his conversations with the priest. Most likely, his plan was to intentionally start a feud with Padraic so that he would be less upset when Colm died, finish one last song, and then kill himself. Since he chooses to escape his burning house at the end of the movie, he likely changed his mind at some point.
He realises at the start of the film he's never going to achieve any sort of standing as a musician beyond being a country fiddler and teacher, reinforced by Padraic's sister informing him he doesn't even know what century famous musicians were born in. He decides to end his own musical career but needs a scapegoat, Padraic, to blame this on.
