How did you or might you react when your partner confesses s/he has been cheating?

I volunteered to officiate his wedding. Good riddance. 

Define "cheating" please.

I would know already.

What? Why on earth would any man with any sense want to cheat on me??? Oh wait, two did - but now I think of it they didn't have a lot of sense :P  LOL one was pretty spectacular in his ability to cheat as we were in an open relationship at the time :P  Now that was a shock!  Generally speaking the emotions went something like, hurt, feeling betrayed, incredulous, very disappointed and disillusioned with the person concerned...

I do think though that that said I would be able to discuss it with the person, to hear them out, find out their reasons and reasoning.. trouble is in situs like that by the point they have done what they have done it's too late to discuss and they feel defensive and not much into talking.. 

On a wider scale I don't necessarily think that cheating is the end - well unless the one who has cheated has decided they want to move on. 

That would probably be the end of the relationship.  However, as I get older and sex is less and less a part of my life, I may change my mind.

In reading your question and considering my answer, I realize that that has never happened to me with any woman I've known in my entire life.