Infidelity? For me its the ultimate betrayal. I can understand a drunken one night stand where the person that cheated immediately admitted to doing it. Anything else and you are essentially stealing choice from your partner. They are living a life based on an assumption of loyalty and you are allowing them to do so knowing that its a lie. Its choice theft and betrayal. On top of that, all trust would be dead. I don't want to have to spend my whole life worrying what my wife is doing if she is running an hour late from work or going out with friends. I am naturally a loner so could adapt to being alone and be quite happy relatively quickly. This is not a knock on my wife, she is amazing and I very much prefer her company to that of my own.

If someone does not confess or cheats multiple times or even worse has an affair I believe that is one of the worst things you can do to a person short of the obvious things like murder, violence, etc.

For me personally there can be no forgiveness. I'm not the moral police though, everyone is free to forgive as they want. If someone is cheated on and feels that its not a show stopper then that's their choice, I'm not them. This is very much just a personal thing, for which there can be no forgiveness. Divorce and separate lives is the only option. I would of course still co-parent my kids with them and be civil (similar to how I interact with my kids teachers) but any emotional attachment would die. I would tell the kids why we are divorcing when they are old enough. This may just be a me thing its very easy for me to do the whole "dead to me" thing and just move on.