Sequel? This doesn't need a sequel. We all know Lois closes her window and Clark flies off, hurt and needing comfort. He'll give up being the superhero and content himself with spending his days with Mayson Drake, who didn't care for Superman anyway.
Meanwhile, Lois will stay mad for a very long time, get a short haircut in revenge, and fly off to Minnesota for a get-away where she meets this bearded guy who plays a guitar. They fall for each other and live happily ever after.
As for the letter, awwww.
Poor clueless Clark hadn't realized he'd put his best friend through all seven rings of hell. Love the part where he doesn't try to rationalize away his keeping of the secret, but merely puts himself at her mercy. We'll see in the next part if Lois actually does open the window. But if she does, how would the next section take the form of a letter? Diary, perhaps? I guess I'll go find out.
Nice job!