Oooh! You managed to capture at least three of my fanfic pet peeves in just two paragraphs! I SO have to do this!
I'm just going to bold any changes I would make (I usually bold, then change the color to something other than black--same color for all corrections and/or comments), and then put any comments in bold, with parenthesis around them. For the most part, everything I've said/changed is just a suggestion, but there are some things (like spelling, punctuation and grammar) which really should not be ignored--although you definitely have the right to do so, against my advice.
Lois was in love with Superman. She also liked Lex Luthor. He was a handsome man, and took her nice places. How could she decide? Sadly, Lois thought that she would never (might want to add "be able to" here) choose. (New paragraph.) Then there was a knock on her door. It was Clark! (How would she know? She hasn't opened the door yet. Did she look through the peep hole, or is she just psychic? New paragraph.) "Come in," Lois said, and he did. (New paragraph.) "Lois, I love you!" said Clark. This made Lois happy. (New paragraph.) "Clark, I love you too!" she said. She frowned. (Would flow better if it was, "she said, then frowned.") "But also Lex and Superman." (New paragraph.) "Well, I am Superman," said Clark. He spun into his costume to show her. (New paragraph.) Lois giggled. "Are you Lex too?"
"No," said Clark. Only a super man (If it's the name, then it's capitalized and one word. If he's saying he's super and male, then it's two words and lower-case.) who loves you!
The End
(Very cute. You could use a little more detail though. One way to go about adding detail would be to do what I did in the middle there--reread your story as though you've never read it before, and if there's something you "don't know" about it, ask yourself a question which you would then answer within the narrative.
Also, you must make a new paragraph every time a new person is speaking. This is NOT negotiable. It is absolutely necessary and required, especially if you want your dialogue to be taken seriously--or at least so the reader won't get confused in the middle of it!
You've done a good job with keeping it to Lois's point of view though. You wouldn't believe how many stories I've read in the past where it seems every other sentence--and sometimes every other phrase--is obviously from someone else's POV, so props for that!
Finally--and this is just a stylistic thing based on my own overly-opinionated convictions about writing--if you've written the story well enough, you really don't need to say, "The End." The tone of the concluding paragraph(s) of your work should already tell the reader that it's the end of the story, without you saying so.)
