This love triangle is the main focus of season 3B.
The Complications of Matenna
During the third season, Matty and Jenna's non-secret relationship becomes more frequently intense, as Jenna never told Matty about her pregnancy scare. The relationship also complicates as Matty has a fight with his parents and moves in with the Hamilton Family, making it increasingly uncomfortable for Jenna to get any privacy and Matty taking advantage of Lacey and Kevin's good nature. However Matty moves back in with his parents and he and Jenna continue their relationship.
Jenna's Feelings Collin
Jenna begins to develop romantic and sexual feelings for Collin after her reading in Bean There, Done That. She then begins to fuel her sex life with Matty by imagining Collin, but she begins to feel guilty about this and talks with her best friend Tamara Kaplan who openly admits it's okay. Jenna starts to ignore Collin's "flirting", but ends up going to an event with him, instead of going to Tamara's party with Matty, after Matty admitted to her that he was embarrassed off her because of the misunderstood failed suicide attempt.
After the event, Collin drops Jenna off in his car at Tamara's party. They talk for a bit and then they kiss, but Matty arrives leaving it unknown to the viewers if he saw them kiss. In the next episode, it's revealed that Matty didn't find out but Jenna becomes addicted to Collin and kisses him in secret, until Tamara catches them. She tries her best to keep Jenna's secret because of "girl code" and also gives Jenna a chance to end the affair. But she becomes hooked on Collin and they kiss on their way into Jenna's home (becuase she thought her parents were out of town for her birthday) and Ming, Lissa, Lacey, Kevin, Val, Jake, Fred and Matty yell surprise, shocking Jenna and themselves at what they've witnesses.
Later on, after the events of the party Jenna's friends piece together the events of what happened and they discover that Matty tried to get an explanation from Jenna and that Tamara punched Collin in the face. Jenna also makes the heartbreaking decision to end the relationship, with Matty.
Jollin and the Beginning of the New Jenna
After three weeks, Jenna begins a relationship with Collin, much to everyone's disproval and hurting Matty's feelings. Jenna wants everyone to give Collin a chance and invites everyone (excluding Matty) to a BBQ, but Jake finds out about Tamara's secret and breaks up with delying her and Ming's invitation to Jenna's BBQ, making Jenna angry and calling her friends "unloyal" and Jake her "slopey seconds" and later the fight turns into a text war. She later becomes alienated by them, and even becomes mean to Matty, who tries to be sympathetic towards her. She gets Val fired, because she suspended her from school after catching her smoking on campus, so Jenna gets revenge on her and gets Mr. Hart to print a cruel article about her.
Jenna eventually becomes far more reckless and sleeps with Collin out of fear of losing him, and disobeying her parent's rules by staying out partying with Collin and his former girlfriend, Angelique Welch, even almost engaging in a threesome with them, but she leaves club without them, leaving them kissing each other and asks Matty to pick her up.
The End of Jollin and the New JennaAfter the morning of her partying, she begins to regret but slowly begins to make amends with her parents and friends, even making a new friend called Bailey. But she realizes that the article has now went out and Valerie has been fired. She campaigns for Val's return with a little help from her mother, Matty and Bailey. Even Sadie Saxton pitched in to help. She later has a talk with Collin, who claims that their relationship was never exclusive and just an affair, angering Jenna and calling him an "asshole." She later becomes smitten after believing Matty will ask her to the dance, but he reveals it being Bailey. She is clearly upset but allows him because she wants him to be happy. She goes to the dance, alone anyway and shares a dance with Matty. She later dances on her own, having fun by herself, knowing that her friends are happy.
- The main antagonists of this love triangle and Season 3 were Jenna and Collin.