Mark Cyr (portrayed by Jason Ritter) is Amber's favorite English teacher who has a romantic relationship with Sarah. Mark is 12 years younger than Sarah. They have an on-again-off-again relationship. He appears in Seasons 1, 2, 3, and 4, and also makes guest appearances in Seasons 5 and 6.
Life
Season 1
Mark and Sarah Braverman get to know each other and start dating much to the dismay of Sarah's kids, Amber Holt and Drew Holt. Though things initially go well, Sarah realizes the affect that their relationship has on Amber, so she breaks up with Mark, hoping that they will be able to date once Amber has graduated from high school. Mark is upset and doesn't want to wait, but Sarah sticks to her decision for the kids.
Season 2
Mark is not heard from too much until Episode 18, where he and Sarah restore their friendship after he offers to read a draft of her play. They begin spending more time with each other as friends.
Season 3
Mark and Sarah get back together after he helps her with her play. Their relationship quickly grows serious, despite some negative ramifications and reactions from others. Despite Sarah's jack-ass of an ex-husband, Seth Holt, coming back into their lives, Mark decides to stick around. Towards the end of the season, they begin talking about having a baby together, but Sarah later realizes that she doesn't want another child. In the last episode, at Crosby and Jasmine's wedding, Mark proposes to Sarah, to which she accepts!!
Season 4
Sarah and Mark are stronger than ever as the whole family celebrates their engagement by including Mark in the family photo. Sarah and Drew move in to Mark's apartment in Episode 6. Soon, their relationship is strained when Sarah becomes attracted to her boss, Hank Rizzoli. In Episode 10, Sarah puts Hank before Mark when she lies to Mark so that Hank can reconnect with his daughter, Ruby. Mark finally gives up on their relationship and breaks off the engagement. He later tries to reconcile with Sarah in Episode 15, but she decides to make it work with Hank instead.
Season 5
Mark runs into Amber on the street in Episode 19. Soon after, he calls Sarah and asks her to lunch. After some small talk, Mark tells Sarah that he met someone and is now engaged. He wanted her to hear it from him, and she congratulates him.
Season 6
Sarah and Mark run into each other at Ruby's school musical. When they run into each other a second time that weekend, they decide to catch up, and Mark reveals that he is now happily married and expecting a baby.