Question: Whose baby is it? The therapist is pregnant. We know she lies at times. I choose to believe it belongs to Bill, evidenced by deep love and mourning showing in the therapist's face at the funeral.
Peri424
9th Feb 2018
The Departed (2006)
Answer: She says "and I thought I was the liar".
Answer: Matt Damon was shown to be impotent, so the assumptions is that its Leonardo's.
He isn't. He's shown to have a single instance of what can be assumed to be erectile dysfunction.
Answer: It's reasonable to assume it was Colin's.
Answer: I think this was left purposefully ambiguous so as to allow the viewer to draw their own conclusions. Is it Billy's? - and therefore Madelyn will be forced to raise a baby on her own and explain the death of its father? Or is it Colin's? - and therefore Madelyn will be forced to raise a baby alongside him, knowing what kind of man its father is. I interpreted the scene as the baby being Colin's. Furthermore, it is not implied that Colin is impotent, only that he has performance issues every once and a while (this could be due to the immense stress and pressure he is under living in constant fear of being made as Costello's rat).
Answer: It isn't definitively answered but it is heavily implied the father of the baby is Billy.
BaconIsMyBFF