Ending is hard... you want to wrap up the plot, and make it emotionally satisfying. And the ending (last scene, last image, last sentence) is what people will remember -- so, what's the main point of your story? Love conquers all? Keep on truckin'? <g> Try to find a way to re-enforce that theme.
You can also try to bring things full-circle -- if the beginning was alt-Clark being all lonely in an empty apartment, the ending might be alt-Clark and Lois in an apartment brimming with light and warmth.
Sometimes it helps to sort of "zoom out" with your narrative camera -- you've been showing every detail in the conclusion of the story. The last few sentences/paras can be a little more pulled back, generalizing instead of focusing on details. Show the big picture (which can fit with the full-circle thing above).
If that makes any sense
Apart from Beginnings and Middles, Endings are definitely the hardest part to write
PJ
