Oh, you have no idea. Blaine cheated on Kurt while he was in New York, REPEATEDLY; Kurt dumped him, they reconciled as friends at Christmas, and then Blaine became convinced that they were actually soul mates after they slept together at Will and Emma's wedding.

Rachel started a new relationship with a guy, and then the writers derailed it by having him be secretly prostituting himself to pay his way through college. Because they couldn't come up with a legitimate reason for them to be broken up. Rachel found out and slut-shamed him, and then Finn found out and beat the shit out of him for "touching [Finn's] future wife."