Brian & Jillian is a romantic subplot that lasted the from Season 5 to 6 and got closure in Season 8's "The Mortician". They arc's main plot is focused on Brian Griffin and his new ditzy blonde girlfriend Jillian Russel-Wilcox.
Arc Summery[]
Prologue[]
The arc first started in Season 5's "Whistle While Your Wife Works". With Brian telling Stewie that he has been dating Jillian as a reason as to why he's not hanging with Stewie as much, but he doesn’t want Stewie to meet her. Stewie is convinced that the reason for this is that Jillian is ugly, but Brian finally introduces Stewie to Jillian to prove that she is actually attractive. Stewie soon discovers that the real reason Brian didn’t want him to meet Jillian is because she is a stereotypical "dumb blonde". Brian is teased by Lois for dating someone so dense when Stewie tricks her into coming over to the house for dinner, and Brian later admits that the relationship is based on sex and that he should end it soon. Stewie encourages Brian to break up with her, but when Brian goes to her house to do so while Stewie waits in the car, he is distracted by her nudity and ends up having sex with her instead. Waiting in Brian's car, Stewie apparently anticipated this when Brian returns to his car three hours later, so he mocks Brian to the tune of Gary Numan's "Cars", much to Brian's annoyance.
The rest of the season had Jillian and Brian seen together in multiple episode like "Prick Up Your Ears", "Love and Sabotage", and "Not All Dogs Go to Heaven" for a few examples, as ways to show them being a true dating couple.
In Season 6's "Dog and Dumber", Brian was drinking his misery away again at the Cabana Club because of problems with Jillian. He actually went there the same night Frank Sinatra Jr. sang there and allowed Brian start singing with him again, leading Brian to believe that he and Frank Sinatra Jr.'s singing together can be a gateway to fame. When Frank says that he's leaving town to go to his next stop on his tour, Brian decides that he wants to go with him, which Frank is happy to agree with. Brian leaves his old life in Quahog behind and goes on tour with Frank. However, during one of the nights, Brian gets head injury while drunk, leading to his intelligence being melted to Jillian's level. He got dumbed down so much that when Stewie tried to pull the "Cool hWhip" on him, but Brian accepts it due to being stupid. While he was able to gain his intelligence back, Brian did note he got a semi-better understanding of Jillian.
Breaking Up[]
The relationship took a turn for the worse in "Movin' Out (Brian's Song)". In it, Brian turns down a chance to see Disney on Ice with Jillian to work on his crappy novel Faster Than the Speed of Love, so he decides to give his ticket to Peter. After Peter and Jillian spend the entire day together and greatly enjoy each other's company, Peter convinces Jillian to either force Brian to let her move in with him or leave him. Brian agrees to get an apartment with Jillian. Much to his surprise, Brian has a good time living with Jillian, but he comes to the realization that there is no way he can pay the rent by himself and he decides to allow Stewie to move in with them, who now makes money with his own paper route. Brian does not tell Jillian that Stewie is helping with the rent, rather he tells her Stewie misses him. Stewie quickly gets in the way of Brian and Jillian's happiness living together and after arguing with Brian one night, Stewie reveals that he is paying half the rent, prompting Brian to admit he never wanted to move in with Jillian at all.
Heartbroken, Jillian leaves Brian. After many failed attempts to lift a saddened Brian's spirits, Stewie convinces Brian to try to get Jillian back. Brian goes to her apartment, only to find that she has now moved in with Mayor Adam West. As the two go their separate ways, Brian moves back in with the Griffins, where he manages to move on with his life.
In "We Love You, Conrad", Jillian showed to move on as well, as she invited the Griffins, and B. Ryan, but not Brian, to her wedding to Derek Wilcox. She asks Peter to make a speech for her, and ends up being the DJ and the one who walks her down the aisle. This is because both of her parents are dead, her mom dying of cancer. She allows Brian and Stewie to meet Derek over dinner at Qu'Est-ce que pue Restaurant, and get to know him. Brian is angered by how impressive Derek is. At the advice of Lauren Conrad, Brian crashes their wedding to object to her marriage and proclaim his love for her, but Jillian lets him down softly and goes ahead with marrying Derek. The newlyweds are then seen having sex at the reception.
Her relationship with Derek didn't last long as her husband Derek was murdered by Diane Simmons in "And Then There Were Fewer", Diane innocently consoles her after Derek's death. The extended DVD version reveals Jillian to be pregnant.
Epilogue[]
In "The Mortician", Derek Wilcox, along with everyone else who was murdered by Diane, had a funeral and Brian tried to seize this opportunity and sees this as his last chance at getting back together with Jillian. However, she never did because Brian realized he was being a bit of a prick, taking advantage of a grieving woman who just recently lost her husband for only to get into her pants.
And aside from Glenn Quagmire dating Jillian to cause Brian pain in "Tiegs for Two", the arc Brian and Jillian had was effectively over from this point on.