Dominic

He killed himself.

He got disappointed with Colin Farrell.

After he did a desperate effort for the girl, and after she turned him down, he realized that he is a lost soul with nothing really to look forward to... Continuing to be abused and hit by his own father, while remaining as the village idiot that no girl will ever love...

He decided to end it for himself.

I guess it was left unexplained but whatever happened, it concluded with his father being haunted by his actions towards his son (and perhaps others) for the rest of his life. As hardened and abusive as he was, his facial expression suggested a guilty conscience.

I thought it left a bit to the imagination...I even think it left room for the old witch to have killed him with her hooked cane...

After all, he seemed to spend a lot of time at shore she also lived right by...

suicide i thought

His daddy was regularly diddling and beating him and the only nice girl on the entire island rejected his advances. I would have killed myself, too.