This sounds a bit like AnnieM's Playing Series. It's not so much a party as it is Paul inviting her out on a double date to catch up. Lois needs Clark to play the part of her boyfriend.
![wink wink](/ubb/images/graemlins/default/wink.gif)
In the later stories in the series, there is indeed a party-type event in which there's a confrontation between Paul and Clark. Hope this is what you're looking for. If not, you should read these anyway.
![goofy goofy](/ubb/images/graemlins/default/goofysmile.gif)
Here are the links for the stories in the order they were written.
Playing the Part Playing to Win Playing for Keeps Playing by Heart Sara
![smile smile](/ubb/images/graemlins/default/smile.gif)