Jo and Alaric
Alaric's good looks helped him wind up in several relationships throughout the show's run. Unfortunately, Kai brought this one to a grinding halt.
Jenna and Alaric
Aunt Jenna was dating Alaric early in the show's run and they were great together. If there was no supernatural forces in Mystic Falls, they would probably still be a thing.
Stefan and Valerie
Stefan has a knack for hiding past relationships from his lovers. His short-lived relationship with Valerie was full of tragedy, but you could tell there was something between them. That's probably why they made a go of things again all those years later.
Stefan and Rebekah
Part of the reason Rebekah became such an intriguing character was that she shared a lot of history with Stefan, who was still pining after Elena. Watching the layers of their relationship unfold in flashbacks was great and the whole pairing pissed Elena off, so there's that.
Stefan and Katherine
Stefan was really starting to feel something for Katherine back in Season 5. Heck, he even managed to stop her from throwing herself off the bell tower when she was human. They have a lot of history and a whole lot of chemistry.
Bonnie and Enzo
Bonnie and Enzo were such a random pairing on The Vampire Diaries Season 7. It was clear they really loved each other, but it's just a shame Arkadius was around and Stefan opted to make Enzo part with his heart. Will they get a happy ending in the afterlife? Probably.