<human>: I'll try to be brief. I'm 26(m), she's 28, engaged 2 months, together 2.5 years, to be married in February w/ date set.  
  
...And I screwed up 2 years ago at a party. Got too drunk playing a stupid drinking game and ended up partly naked with a partly naked sexy coed sitting on my lap. We made out a little at the party. I was too drunk and dumb to extricate myself from the situation. After the party found out she lived in my part of town so of course it was convenient for her to take me home (I was still wasted and horny). Well, we went to her house instead and did some stuff. No sex, mainly making out and groping which ended as soon as I sobered up. Never saw each other or spoke of it again.  
  
The end? No. Here are some more facts.  
  
Most of my best men were at this party. I only got one question about "WTF are you doing, man?" and it wasn't even an angry question, just a confused one. My story to the guys was we just did the dumb things they all saw at the party and then she just took me home. The tangled web of connections is irrelevant, but somehow her story got into the mix and now they all probably know what I did.  
  
I'm a good man, I treat my fiancé amazingly, and I plan to forever. This is truly my first adulterous act of my life, and I've regretted it ever since to the point of many sleepless nights.  
  
I read a bit about cheating at the time and most of the advice was: "If there is practically 0% chance of her ever finding out, and you never do it again, take it to the grave." But now, with the best men knowing more than I thought, and the "Speak now or forever hold your peace" question coming up, the chance may be closer to like 5%. Maybe 10% chance of someone accidentally hinting at it and then me not being able to withstand questioning from her.    
  
What should I do?

Can you give me a shortened version of the text?
<bot>: Messed up at a party early in my relationship and thought my secret was safe, but it may not be as secure as I hoped. Should I still take my mistake to the grave?