Things start to click betweek Sean and Will when Sean opens up about his wife and the things he misses about her. In a Carpe Diem moment he tells Will to love like he's never loved and all that, and not to be afraid of the future.
So Will seeks out Skylar (not the bad guy from Heroes, but Minnie Driver before she had some work done), apologises for not calling, and falls in love.
Things are going well in good old 'Act Two' fashion, until Skylar asks Will to join her when she moves to California at the end of the semester. Will has never left the State and fears the future at the best of times, and when he refuses the conversation turns to his past. Will storms out of the dorm and tells Skylar he never loved her, leaving her an emotional wreck.
Still revved up, Will meets with Prof Lambeau, who has been trying to set him up with some great jobs, and wants out. He belittles the Professor and leaves.
It's then up to good old Chuckie (Ben Affleck) to tell Will some home truths that Will is meant for a better life -- and that every morning when he walks up the path to his door, he hopes he has left and started on the road to a better life. -- It's the one original bit of the movie where his friends haven't been dragging him down (like some of the DVD back-cover plot synopsis will tell you), but been supporting their troubled friend all along. They even pitch in together to buy him a beat-up old car for his 21st birthday.
Will goes back to Sean one last time, and they talk openly about the past and the abuse they both suffered at the hands of evil men. Sean holds Will and tells him "It's not your fault". He repeats it until it hits home and the floodgates open.
Will accepts a good Government job from one of Lambeau's contacts ... yet changes his mind on his first morning. Instead he drives by Sean's apartment and leaves him a note ...
Scribbled in crayon, and in a 5 year old's handwriting (the weirdest bit of the movie!), is a few lines that he has decided to say goodbye ... and to 'go see about a girl' using Sean's reason for missing the World Series back in the day and meeting his future wife.
Chuckie calls for his friend that morning ... and is happy to see that he has left. Little Casey Affleck is also happy that he can call shotgun now, and moves up the 'best friend' ladder to sit in the front.
As it ends, Will hits the highway heading to sunny California.