I often say that Think Before You Think is more of a spontaneous series of events than something with a "plot." Nevertheless, here is a list of notable events that are relevant to the progression of the comic. This leaves out a lot of stuff about character development.
Psychic - Julia and Becky find out that Brian can read minds.
It Was Going So Well - Kevin, Sarah's old supervisor, shows up at the cafe where she's currently working and starts berating her. It turns out Kate, Sarah's current manager, knows what happened at her old job, and she kicks him out of the cafe.
Resentment - Sarah talks to Damien, her counselor, about her encounter with Kevin, which leads to a series of small misunderstandings when she talks to Brian.
Deep Dark Secrets - Selene and Benson are talking after their group, After Selene reveals that she wants to be dominated, Benson almost rapes her, but Brian comes in and stops him.
In a Corner - Brian slips up when talking to Selene, and after that he reveals to her that he can read minds.
Julia's New Job - Julia starts working at Burger Ace. Isaac warns her about what happened with Sarah there. She finds out that Kevin is no longer working there, in fact he was fired after all of his employees quit and the branch temorarily closed.
Brian Comes Back - Brian comes back. Julia is confused about her feelings because of the stuff that she had talked about with Jason earlier. Brian starts working at the cafe again.
Mental Probing - After "talking to" Jason, Brian realizes that after leaving Julia in the fall, he's going to have to earn her trust back. They decide to go on a date.
Moving Day - Julia and Becky move into their new apartment. Jason goes home for the summer.
Airport Memories - Brian and Julia go on their date, and Brian mentions that he thinks Julia is more committed to the relationship than he is, which upsets her.
Being Mean - Things get tense between Ethan and Sarah. Brian talks to Julia and says he didn't really mean that he was more committed than her.
Rescue Romance - Brian and Julia decide that they're back together, and they can continue to work out their relationship insecurities.
Knowing Someone - Julia finds out that Becky had sex with a girl (June) and is bisexual.
A Hard Conversation - After getting in a fight, Ethan says he doesn't like being with Sarah. She vaguely threatens to do something drastic if he leaves, and he agrees to stay with her.
Brian Helping Out - Julia's sister Annie moves into her old dorm. Her roommate is Selene, Brian's old counseling group member. Brian tells Julia that she knows he can read minds, and admits that he is somewhat attracted to her while reassuring Julia that that doesn't affect how he feels about Julia.
Dr. Morgan - Sarah starts seeing a new counselor, Dr. Morgan.
The School Nurse - After Brian starts his new high school counselor job, a kid comes to see him after getting beat up. Brian tries to take him to the school nurse, but she won't help him, and it becomes evident that the school isn't addressing the bullying situation effectively.