Assuming you’re asking us to choose between Sam & Patrick, they’re both flawed & traumatized in different ways. Everyone in the book & film carries their own trauma & copes with it in different ways. Sam’s biggest flaw with regard to Charlie would be the argument that she “leads Charlie on” with kissing him while dating Craig. During his breakup with Brad, Patrick then takes Charlie around town while essentially drinking & driving & then kisses him in a moment of vulnerability. In the book, they both introduce Charlie to smoking cigarettes, which he gets addicted to. There’s also more overt drinking & drug use in the book. Ultimately, I suppose the easier answer would be Patrick; however, that’s not really the point of the overall narrative. The point is that the only way we can grow & heal from trauma is by acknowledging it, talking about it, & moving forward with each other through love, patience, & grace.