Pretty Little Liars is about as chock-full of drama as a series can possibly be. Four high school students are stalked by a psycho, who ruins their lives when they're not actively ruining things on their own.
One area of drama the show makes time for is in romantic relationships. Though it's pretty clear Hanna will end up with Caleb, Spencer will end up with Toby, and Aria will end up with her teacher (one of the most problematic things about the show), there are plenty of pit stops along the way.
Aria & Noel
Aria agrees to a date with Noel before she's over Ezra, signifying to all that this relationship wouldn't last. When things officially end with Ezra, she becomes more serious about dating Noel. Aside from Aria's feelings for Ezra, she's also hiding the fact that she and her friends are being stalked by "A".
However, it later turns out that Noel is just as shady. He finds out about Aria and Ezra and tries to use the information to blackmail Ezra into giving him better grades.
Emily & Paige
When Emily and Paige first start dating, Emily abruptly ends things because she doesn't want to date someone who's still in the closet. When Paige tries to date a guy, she confides in Emily how wrong it felt and how afraid she is to come out. Once again, Paige tries to keep their relationship hidden, prompting Emily to end things (seemingly for good). They finally get together for real when an intoxicated Emily wanders over to Paige and kisses her. They date for a while until Paige betrays Emily by giving information to the police about her friend Alison.
They later get back together, but Paige's parents want her to move to California since Rosewood seems to be the most dangerous place in the world. Their relationship can't handle the distance. Years later, they give things one last try, but then Emily decided to have a baby with Allison, effectively ending their relationship (seemingly) for good. Their relationship survived many ups and downs, but ever since Paige tried to drown Emily in the pool, it was hard to believe they would end up together.
Aria & Jake
Aria meets Jake when he offers to give her self-defense lessons. She kisses him during one session but says it was a mistake. They start hanging out, and she's able to confide in him about her whole messy situation with Ezra. Since they don't make things official, Jake is free to see other people, and Aria sees him with someone else.
Her jealousy makes her realize that she wants to be exclusive. They officially start a relationship, which later ends when Aria gets back together with Ezra. Jake was probably the healthiest choice for Aria to be with, which made it clear from the beginning that she wouldn't end up with him.
Emily & Samara
Samara is one of the first people with whom Emily feels she can be really open about her sexuality. The two eventually start dating. Emily's mom even likes Samara, and Samara helps Emily get out of going to a college she doesn't really want to go to. Emily finds out that Samara is seeing someone else, and confronts her.
Samara states that they hadn't yet made things exclusive, so she felt it was alright, but introduces Emily to her friends. She breaks up with Emily when she finds out that Emily asked one of her friends out.
Hanna & Travis
Hanna starts dating Travis before Alison comes back to Rosewood High. When she does come back, she confides in Travis about her anxieties about the situation, and Travis is sympathetic but doesn't really get it.
He struggles to deal with how overly complicated Hanna's life is, and how much it seems to revolve around Alison. When Caleb returns to Rosewood, Hanna is clearly still in love with him, and Travis breaks up with her.
Hanna & Jordan
Jordan is the classic "fiancé that's definitely going to get dumped when the protagonist reconnects with her high school sweetheart, a classic Hallmark movie trope.
He's super nice, and rich, and absent. Just like every other non-Caleb love interest Hanna has, everyone knows it won't last. They break up, and she ends up marrying Caleb.
Spencer & Caleb
Spencer and Caleb start dating after a one-night stand. They're happy together, and they have a lot in common, both being the "smart ones" of the group, but their relationship obviously bothers Hanna, Caleb's ex, and Spencer's best friend.
It becomes increasingly clear that Caleb still has feelings for Hanna, and he kisses her while still with Spencer. He also can't tell Spencer that he doesn't have feelings for Hanna. They break up because Spencer loves him and doesn't believe that he loves her.
Aria & Andrew
Andrew is tutoring Aria while she is still, of course, involved with Ezra. They kiss when he comforts her after she's hurt herself due to some classic A sabotage. They have a sort of ill-defined relationship from that point.
When Aria and her friends accuse Andrew of kidnapping them, he's arrested. He didn't do it, and he's obviously pretty mad that they falsely accused him. This effectively ends whatever he and Aria had going on.
Emily & Talia
Emily and Talia share a mutual attraction, but Talia has secrets of her own. Her secret is that she's married, which is a significantly less intense secret than Emily's, which is that she and her friends are regularly stalked by a violent psychopath whose identity remains unknown. Things end when Emily discovers that Talia was just "trying out" girls by seeing Emily.
Emily & Sara
Sara and Emily's first kiss is an indication of how weird their relationship is. After escaping the dollhouse, Emily and the girls realize they've been microchipped.
Emily tries to check Sara for one while she's sleeping, so Sara wakes up and kisses her, and they end up making out? Later, in the most obvious twist of all time, Sara is revealed to have been working for A. She's later murdered, so, no chance of reconciliation there.