Call me a sucker but I really bought the love story. Affection really grows out of hardshiip. Especially when those involved are lonely messed up people.
The father-son relationship on the other hand had no convincing resolution and no bearing on the story whatsoever. The former because, hey they're both safe now, they can go back to hating each other next week. The later because with a little tweaking you could tell the exact same story with the two getting along but still struggling with the loss of the mother. 99% of the movie was completely incidental to them hating each other.