I'm fairly.pragmatic about these things.
In reality, some people are sexually incontinent. Either because they dont value fidelity and don't consider it important to remain faithful if they see someone who catches their eye, or will actively pursue affairs. These people are the ones who will go through life and relationships cheating without thought or consideration, promise never to do it again and then carry on and hide it better.
Some people through their own moral standpoint will just never do it.
Some people will believe that they're not capable of it and might be right for years but a moment of weakness or vulnerability comes along, or a period of not having safeguarded their relationship carefully, and make an error in judgement or a mistake or just get caught up.on things, deeply regret it and resolve to never let it happen again.
Everyone I know who has ever cheated, fell into the latter group.
My dad had an affair. He left, he married her and they had 20+ years together until he died. He didnt cheat on her. He'd just ben desperately unhappy in his marriage to my mum (for context, my sibling and I are now nc with her and he stayed in the marriage until we were late teens to protect us).
My exh also had an affair. They have now been together for 14 years and I know that he won't have cheated on her because he's not 'a cheater'. But our marriage was in a bad place and my mum's behaviour had a huge impact on us and my dad dying was the final straw for both of us really. It gave us both chance to be happy.
I went out with someone a few years ago who admitted similar to this man has admitted to you. He told me early on, as this man has told you. He was very contrite, had obviously done a huge amount of self reflection, regretted it immensely for the harm it had caused his ex and what it had revealed about him.
We spit up for other reasons but, in some ways, but i was as confident as I could be about anyone that he wouldn't cheat because I could see how it had affected him.
People will say a leopard doesn't change its spots, which is overly simplistic. Lots of people dont realise they could be vulnerable to an affair if they've never been in the position. The people I've detailed above werent in happy relationships. They had been at one point but life had overwhelmed them and they made the wrong choice. Does that make it ok?
No. Of course not. Conversations, splitting up are all far better options but the reality is that humans are flawed and there will even be people who insist they've never had an affair who have done because they can justify why they did it to themselves and so dont consider it in the same league as people who just go out on the pull when they're married or because they dont like what it reveals about themselves.
I also disagree with the 'laying the groundwork' comment. Yes, some people will be telling you 'who they are' (don't give me enough sex and I'll look elsewhere; I'll shag about and when you challenge me on it, I'll tell you that you knew i was like this from the start) and other people will be saying, I was in an untenable situation for a long time. I should have handled it diferently and but I didn't. I made the wrong choice at the time but I regret it and I wouldn't do it again.
There is also a third option: OP holds out for someone who has not already declared himself to be a cheater and actually isnt a cheater. They do exist.
That is true but no one actually knows if they've met this person or the one who has cheated and is lying.
It's a bit of the proof of the pudding is in the eating situation.
Basically, OP, unless someone is communicating generally that they don't value monogamy or is spouting shit about men needing variety or whatever, or is behaving inappropriately with other women when you're out together etc, you have no way of knowing whether someone will cheat on you or even has until/unless you discover an affair.
And someone not having had an affair previously is no guarantee that they won't in the future if the conditions are right.
So you have to judge someone based on what you believe is their position now.