I'd love to see a fic in which their no strings attached, kinky and often violent affair kinda backfires on them. Because Clark eventually realises that just fucking and pretending that he doesn't have feelings for Bruce doesn't work for him anymore. And because Bruce sucks at feelings, he agrees that clearly they need to stop sleeping with each other and spending so much time together (because he's crazy about Clark, but it's not like Clark will ever be happy with him, right?). Cue painful breakup. Preferably with an eventual reconciliation, however you can make that happen. I just want to cry a lot first. ;)