Relationships

How can someone make it ok to cheat in one relationship, but not the other, if so? What am I missing?

I wonder how it was possible for my ex to tell me he would dump his girlfriend if I took him back, or too him leaving a girlfriend because he said she wasn't like me, that I saw no sign of him being able to cheat (on me) when we were on?

Had another experience that someone who wanted to be my friend after I said we should not date anymore would get a girlfriend!! just so that I could feel relaxed about our socalled friendship that I didn't want in the first place, but revealing he did that just so I would still be in his life somehow!!. When I did date him I saw nothing like this coming. I never thought he could do such a thing.

I never thought someone I was in a relationship with, serious or maybe about to be, would cheat on me, had it in them, before, when we were on, or after. As individuals.

Either I was terribly naive or they had for some reason decided not to cheat on me so far, but were like this in reality, with another girlfriend? Could that be it?

What I can say about my exes is that they apparently had no trouble getting a girlfriend. My current partner is too some sort of magnet.

After incidents I realized my partner was no cheater, and I've moved on from that, but there is this part of me wondering what did I miss about their characters? I knew them to have flaws, Im sure I have mine too, but I swear it they always behaved right concerning this to me.

My partner vows he has never cheated on someone in his past (but there was pressure he would get back with his ex when he was single and met me, which created a lot of noise/drama behind my back, I knew nothing).

When they would talk to me about this they would say their love for me was different, love of my life'.

I hated the whole scenario and felt bad for the girlfriend, and just couldn't believe it. How is it OK and not OK by them?

Updates
7 mo
Been told that some don't want to be alone and there could be many differences in what a girlfriend is or not, both to the guys and within agreements between them. But to me with these guts that don't sound right, had it been equal, open, they would use the word we. (I have never had trouble being alone and when Im in a relationship Im in it, I've never dated more than 1 simultanously, but know that's common too, especially these days with dating aps).
How can someone make it ok to cheat in one relationship, but not the other, if so? What am I missing?
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