Difficult question to answer

I have recently been asked the following question:

What would you do if you find out that your partner has been cheating behind your back?

I must admit I was a bit floored by the question, probably because I have such a fundamental trust in Sam that has precluded me from ever asking myself that question. My trust in him isn't baseless either - his conduct to date shows his single-mindedness when it comes to me and if either one of us slips up, I doubt it would be him.

But still, the question made me think. What would I do if I find out he has been cheating on me?

I'd like to think I could forgive if he shows remorse but forgiveness doesn't equate 'accept and move on'. I think being cheated on is a violation of many different levels of trust. I'd feel betrayed because I have dedicated myself to him and no one else and I'd feel angry because he has potentially exposed me to life-changing health issues. Worse still, if I am the one who finds out he has been cheating, the dishonesty would call to question the very foundation of our relationship and whether it has effectively ceased without me even knowing about it.

So the best case scenario is - we would yell, we would cry, we would talk, until I could get to the point of forgiveness and give him another chance. But the more likely scenario is that I wouldn't be able to trust him going forward, wondering if he is with someone else every time we are not together, which would be exhausting and untenable. I think the emotional and mental toll would make it impossible for us to ever go back to the way things were, which means that the relationship has been permanently damaged or, even if it could be repaired, permanently scarred.

I have no doubt that I could return to a state of composure with him after a while but I would very likely terminate the relationship and transition it to a friendship shortly after, all the while making practical arrangements to demerge our affairs.

I guess I can say all this but I'd never really know unless something like this actually happens to me. As to what I would do if I were the one who is on the other side of the table - the thought makes my head hurt and I don't even want to think about it.