So this video is a cover of Joni Mitchell's song "River" from her beautiful album, Blue. I warn you that this is not a happy Christmas song, so don't watch it
"River" is a breakup song -- particularly poignant at Christmas -- but what made this version so sad is that RDJ's character has come to the realization that he can either have Ally or he can move back to wherever he came from (New York? Been too long...) to be with his little boy, who lives with the ex-wife. But he can't do both, right now anyway. Somebody's gonna cry, right? And thankfully, RDJ's character does the right thing and moves away so that he can help raise his son and Ally's heart was broken and so was mine.