Heartwarming Moments: Jake's "You won, daddy! You won!" It doesn't matter that Dennis really came in last, hours after the next-to-last person crossed the finish, because he finished, and in his son's eyes, that means he won.
Ho Yay: "Go on, you beautiful man! ...apologies, it's hard not to get caught up in all the excitement."
Moment of Awesome: Dennis, at the halfway point of the Marathon that he's been running for the last eight miles on a badly sprained, and possibly broken ankle, hits the wall, hard. He stands there, motionless except for the swaying, obviously exhausted. And then he crashes through the wall and keeps going to the finish line. Because he promised he would, damn it!
Except reading it as just that means you missed the entire point of the film. He's a decent person who did a stupid thing because he was afraid; completing the marathon, confronting the fact that leaving his fiancée on their wedding day means he's a bit of a shit? It shows he can try to turn things around. And she hasn't even taken him back at the end of the film fully, they're just on much better terms than they were.