Jared offered to fake the emails voluntarily, before Evan asked him to (heck, before Evan even came up with the thought that he could fake the emails), he was the one to argue and convince Evan that he shouldn’t come clean to the Murphys when Evan wanted to, and he produced and sold Connor Murphy memorabilia long before Evan got involved and when asked joined the Connor Project without so much as a protest or comment.
While I do belive part of it is due to his and Evan’s friendship, no matter how much he plays it off as a joke, I also think that on some level he felt at least partly responsible for Connor’s suicide due to the comment he made about his hair the last morning Connor was seen in school and calling him a freak.
In the book we learn that he tells offensive jokes as a coping/shielding mechanism when he feels vulnerable or nervous (he had just finished telling Evan that they were “family friends” on the first day back from the summer, something I can’t imagine him feeling too good about doing) and genuinely can’t help how much of a jerk he comes off as sometimes.
I think that on some level he really did feel like he had something to do with Connor’s death and was looking for ways to atone and compensate for it with Connor’s family. Thanks for coming to me TED talk.