Billy’s and Colin’s respective reactions to Madelyn’s childhood photo

I got the feeling Madelyn was an only child and she treasured her childhood memories because as an only child she was the central focus of them.

You’re right that she might have been subconsciously trying to get Colin to accept having kids in the future. But I simply saw it as a relatively sheltered girl who loved treasuring her childhood memories…memories from a time when maybe she felt more secure and happy.

Colin’s rejection could mean all those things you listed. It is established that he is indeed impotent. The gay angle has been discussed before…given Colin’s overcompensating during the football game against the firemen…calling then queers and homos. It’s possible, but not conclusive.

He might not want to start a family given the immense pressure he’s under and that it could create a bad situation for any future child. Colin had enough decency to understand that he was essentially playing with fire and couldn’t get out of the double agent predicament he had gotten himself into. So exposing a child to the possibility of his/her father being outed as public enemy number one or killed for it…would have been cruel on the kid(s).

Sullivan was immensely insecure…and Costigan was the exact opposite. Costello even began liking Costigan more. He would have killed Costigan if he found out he was a cop…but that would have been for self preservation. If Costello had to choose…he would have chosen Costigan. He didn’t respect Sullivan. He treated Billy like his own boy after beginning to trust him. To the point where Billy could mouth off to French and say “I’m not staying…you can tell him I said that.” Whereas Colin had to grovel and ask for forgiveness when Costello began yelling at him over the phone; “give you?” Give you?” And then Colin had to take a subdued tone and apologize. Costello didn’t respect that kind of groveling behavior. Billy on the other hand threatened Costello to his face if he kept accusing him of being a rat. Costello appreciated and respected such a ballsy move.

Costello made Billy more of a surrogate son than Colin could ever be. Despite the fact that Colin had spent over a decade under Costello’s tutelage and Billy had only been in with Costello for a year. It’s a testament to Billy Costigan’s superior qualities over Colin Sullivan…everyone liked him better. Costello, Queenan, Dignam, Colin’s own girlfriend Madolyn. Billy Costigan was the man Colin Sullivan wished he could be.