They basically conclude that the best thing about the characters was how they defied expectations by never working through their issues or getting a happy ending. Um...yay? But they were soulmates, apparently

Oddly, this concept I kind of adore. Or at least I find it genuinely interesting. Like a lot of the rest of the final season, I don't think it's told well in the end, but I also think it's why Lee and Kara can remain to engaging. They present a fascinating puzzle to unwind because they manage to be both inseparable and unrequited. Because there should be a way to 'fix' their relationship without ruining the two of them.