Do I need to be honest, or can I live by the old saying "Don't ask, don't tell?"?

I recently started a new job, and one of the first things I realized about this place was that there was a lot of hooking up amongst co-workers. I told myself I wasn't going to become a part of this and I have always lived by the old rule "Don't hook up with people from work", but recently I have been getting to know 2 guys there, which I both equally like. One, has an awesome personality and I just love being around him. I feel like he has broken down my wall that I have had up for so long and I am starting to have true feelings for him, but I'm not so sure that's what he wants. Anyway, we ended up having sex and are currently still having "casual sex", but in the very beginning of all this I had sex with the other guy too. : / I know that seems real bad, but I dont usually sleep around like this. Now, we all work together, both guys I believe are interested in me and they both know it, but what they dont know is that I have already slept with both of them. Now, my conscience is eating away at me because I truly feel like this was the wrong thing to do. Although, I am single and they both are too I feel like i should have been honest with both of them. I hate lying and withholding information. I'm afraid of what they might say or do if they happen to find out just through casual conversation with each other. I am considering coming clean with my little secret, but one friend told me I should just say nothing unless it is some day brought up by them. What should I do? I really do care for both of these guys and if nothing else, I'd still like to remain a friend to them....