It would definitely have to depend on the circumstances. I would find it difficult to just throw away a 15-year relationship without trying to work through things a bit.

With marriage it's harder. But I think I would.

There's nothing easy or quick about this answer. I suppose it depends on the situation.

I would say yes. But we've been together for so long that I would find it hard to leave him. We would probably try counceling first.

I hate the idea that sexual fidelity is the Unforgivable Sin in a relationship, when there are so many other ways we can hurt each other. I was far more damaged by my ex-husband being uninterested in sex with me over the course of several years than I would have been by him having an affair.

Probably not. I'd like to try and work through it, he did the same for me when I screwed up and cheated on him years ago.

I would leave no matter what. I might still love that person, but once you've crossed that line of trust...the relationship is done for me. Emotionally, I just couldn't handle being with someone who would hurt me like that. It would always be in the back of my head...

i love my husband way to much to even consider leaving him, but if he ever did cheat (i highly doubt he would) i definitely would grill him and want to know why.
he does joke with me that when i turn 40 (im 22 XD) he'll trade me in for 2 20 year olds. i know he won't, he'll be 68 then.

I voted yes and I think I would but I think I'd be willing to work on it and go to counseling and perhaps get back together if we were able to sort everything out.

trust is very important to me so id probably leave

I'd probably leave. I know for sure I'd flip their shit - it would not be taken lightly, in any case.

I'd leave.

i expect that i would end the relationship, not sure that i would be able to trust them again

It would depend on so many factors, like who they cheated with, why, did they want to reconcile, etc.

I put, "other" before our daughter and engagement, he did have a bit of an indiscretion. It wasn't physical, emotional only, but it was enough that I asked him to leave. At that time though, there were some very serious problems stewing between us that we had both neglected to work on, and the answers to why it happened were very obvious to me, and later him once his head cleared. We made a very strong effort to fix what was wrong, and have been great and better than ever, ever since.

If it happens again though, bye bye, buddy. If he is unable to recognize when things are getting to that point again if they do, and puts him self in a similar position again, I'm done. I do not want to be in a relationship that is on again off again, and I don't want my daughter growing up thinking that's normal. We would, I think, have to have a serious communication failure to get to that point again, and we recognize that so we constantly make sure we're open and talking all the time. BUT if we do fall apart again, it will be the last time.

50/50 might leave might try to work things out

That depends on a lot of things. For instance, are we talking about a one-night stand, or keeping a mistress for years? There would be much discussion before I could reach a decision, and probably counseling.

Other: I'm honestly not sure how I would react (and hopefully won't ever have to find out). My gut instinct is that that would end the relationship, but maybe I'd go the reconciliation route (though I'm not sure I could ever fully trust the person after that).

I would probably leave. 90 percent chance.

Definately wouldn't give him any for a while.

Trust would be broken...I am not sure, I would like to believe I would give her another chance if she truly repented.