The Departed : Why did psychiatrist Madolyn sleep with Billy? Was it his baby?

I can understand Billy's (DiCaprio) motives as he had no family, no friends, had serious emotional and mental health problems, was completely lonely and craved caring for, but Madolyn's motives? She was in a steady, presumably happy relationship with Colin if they moved in together and were planning to get married and start a family. Was she just attracted to Billy's vulnerability in that particular heat of the moment? Did she feel pity for him? Was she just bored? I don't recall her dropping hints that she liked Billy that way, apart from saying she'd lie to Colin if he saw her and Billy together having coffee. Though she seemed deeply devastated at Billy's funeral. Is there any reason to believe the baby could've been Billy's? The film kinda jumps over Colin and Madolyn's relationship and everything is implied (for obvious reasons, as this film is a crime thriller, not a drama romance), and yet Scorsese really intended to include a love scene between Madolyn and Billy as if their 'thing' was more important than her and Colin's. What do you think?

My take is - yes - it COULD be his baby but we will never know. As far as her relationships - I think her pending marriage to Colin was more of a convenience - she saw him as single, good job, good looking, stable, etc (kind of what Baldwin was saying to him at the golf range). She then found Billy who was more honest, exciting, etc - and she fell for him. I think if she had the choice she would end up with Billy - but Colin was a safe choice.

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Colin is leading a double life and the fear and stress makes him uncommunicative and a crappy mate and it also causes his pee-pee to not work. Billy is also leading a double life but he's a much better liar and overall scumbag and he is able to channel all his issues into a believable story that makes her feel he is a vulnerable good guy and his pee pee works great. Madolyn is also terrible psychiatrist a terrible judge of people and a bit of a ho

Yeah but Billy really is the good guy. He can't tell her who is because it will blow his cover. Plus she can see something good in him and then after she reads what's in the envelope I'm sure it reinforced all the feelings she had for him. I think it might be his baby.

i don't know, and probably.

Sullivan was impotent, he had erectile dysfunction. he couldn't perform in bed. thus Madolyn needed another man. sex is the most important thing for women in a relationship, although they deny this fact.

I guess she couldn't feel trust from Sullivan since Sullivan deluded her about his work, also he's not good in bed..Billy was the one that completely opened himself to him and obviously better than Sulivan in bed..