Multi-fandom versions seen everywhere.
1. When wee!Clark touched wee!Lex, an unbreakable bond was established. This unrecognized and unfulfilled bond was at the heart of all their early problems. Along with stubbornness.
2. Clark was not yet an adult when he graduated from MetU. The Kryptonian year is 1.39 times that of Earth. At twenty-one he would be just a little over 15 Kryptonian years. Kryptonians were considered legally adult at 16. Perhaps this explains his often childish behavior during the early years of his association with Lex. Along with his questionable upbringing by the Kents.
3. Clark will eventually return to the Arctic Fortress of Solitude for an extended period to "complete his training" after graduating from MetU. He'll emerge older, wiser and regretful of his teenage years in Smallville.
4. Clark spends another two years as a freelance journalist before returning to Metropolis and applying to the Daily Planet.
5. Clark's reason for returning to Metropolis after his sojourn in the Arctic is to find a way to reunite with Lex.
6. Clark hates the fact that he's "at war" with Lex. But better a battle between them than no contact at all.
7. Lois is the driving force behind any investigation of Lex. Clark's main motivation is to keep himself in Lex's thoughts and to save Lex from his own machinations.
8. Lois really is stupid enough not to recognize Clark as Superman. Despite having seen Clark's beautiful body first hand, she just doesn't see Clark as special enough to be Superman. Clark is relieved in a way and insulted in another.
9. Clark began to stop seeing Lana Lang as the perfect princess when she killed Genevieve Teague and started the whole Zod affair. It took her marriage to Lex to finally open his eyes, though.
10. Lex really thought he loved Lana, but now realizes it was only a way to keep Clark close.
11. Lana left the country when her marriage to Lex ended. She settled in a very small town in France where she runs a cafe. She doesn't dare set foot in Paris or return to the US.
12. Lex has never seriously tried to kill Clark (well, maybe his Alexander side tried). His battles with Clark are a way of keeping Clark in his life.
13. Yes, Lex knows that Clark Kent is Superman. He's not as stupid as Lois Lane.
14. Lex made sure that Lois met Bruce Wayne. She annoys the hell out of Bruce. That amuses Lex.
15. Lex is still afraid that aliens other than Clark will attack Earth. He uses his battles with Clark to keep Clark (and other heroes) ready for the most outlandish possibilities.
16. Lex secretly funds the Justice League. Bruce may be a big source of their budget, but all of the "government funding" comes from Lex.
17. Lex's kryptonite ring is a fake. Clark knows.
18. Mercy and Hope wish Lex and Clark would just drop the facade and move in together. It would make their lives so much easier. And they'd love a ring-side seat when the two start shagging. Mercy really enjoys busting Clark's chops. Hope is running out of ways to hide all of the ways Lex is generous with Clark and his friends.
19. The Fortress AI that Clark met as a teenager was a fake. Only after the Fortress recovered from the battles with Zod and the zoners did the real AI emerge. It was part of Jor-El's crystal Clark got from Raya. But even the real AI tries to run Clark's life.
20. Clark and Lex have had sex -- multiple times. And there was no red!K or sex pollen involved - no matter what stories are told around the Watchtower.