Michonne and Andrea. It sometimes seems like what really bothers Michonne about the whole Woodbury situation is that Andrea started a romantic relationship with the Governor and pushed her to the side.
Despite only knowing her for a few days at best, Princess spends much of "Splinter" deeply concerned for Yumiko's safety after she receives a head injury from one of the Commonwealth soldiers.
Quite of few things that Russell can say ends up with Nate responding in some sort of flirty manner, intentional or not. If all of these possible responses are chosen in one gameplay and you choose to befriend him, Russell's storyline can feel like a quasi-slash fic, much to the pleasure or horror of the player.
From the beginning to end, Nate can possibly come across as being very "friendly". If Russell doesn't hide from Nate and tells him that he needs a ride, Nate will respond by asking if he'll work for it because he has "needs", though he'll soon say that he was joking. When in the car if Russell asks Nate if they can just drive instead of talk, Nate responds with confusion over the plural usage and asks if Russell wants to sit on his lap. He apologizes soon after for freaking him out. At the gas station when they're both getting shot at, if Russell responds with fear, Nate will ask Russell to look at him. If Russell refuses, Nate will cup his chin, not so roughly make Russell look at him, and motivate him to continue on. With all of these moments from Nate and the more friendly actions on Russell's part; accepting the drink, apologizing for being scared, thanking/acknowledging that Nate saves his life when he falls, and staying with him at the end can make this part of the game really enjoyable or disturbing.
In Season 2, Luke and Nick have a few moments like this. Kenny actually comments on this when trying to get a rise out of them.
Also in Season 2, Clementine and Sarah have a few moments which could be interpreted as Puppy Love if you choose to be her friend. One moment in particular when Clementine tries to comfort Sarah in episode 3.
Clementine: You wanna hug?
Clementine: Okay, well I owe you one for later then. You might not know its coming though, but I could just sneak up on you when you're not expecting it.
Kenny and Lee, especially if you're siding with the former on matters.
Episode 5 of Season 3 gives Javi an opportunity for a flirtatious exchange with Jesus.
Season 4 episode 1 gives Clementine ample opportunity to fluster Violet. If they get along, Violet throws her a few shy fond looks. When they converse alone in the bedroom, Violet mentions that she's into girls by evoking her past relationship with Minnie, a.k.a THE go-to tactic for testing the grounds. Clementine can later mention the conversation, saying she really enjoyed getting to know Violet.
Season 4 has Violet, who prior to the final season, was dating one of the twins, Minnie. If you choose to go fishing, you can find a heart graffiti with Violet and Minerva's initials and you'll get the achievement titled "Lost Love". Violet also quickly develops a crush on Clementine, hinted by a few subtle interested looks and her annoyance whenever Louis makes a move on Clem. Brody even lampshades this, when she tells Clem how surprised she is that Violet opened up to her so quickly.
Episode 2 has Violet and Clementine's relationship come full circle, with Violet becoming more open with her feelings after thinking Clem and AJ died by raiders' hands.
When Clem returns to the school, Violet expresses how she lost it when she saw Clem pinned by Lilly, and immediately came to help her.
During the card game, Violet's crush on Clem is pretty obvious. If you say you'll marry Ruby, she'll tell Aasim that Clem is a better catch than him. If you say you'll flip Ruby, she stays quiet but has a curious look. If you say you have a crush on someone, the camera will pan to her looking curious again.