Your husband (future or current) meets a girl who's objectively very physically attractive. She's deeply into him. He rejects her advances because he's committed to you but knows deep down that if it weren't for you he'd love to sleep with her.

So he rejects her but at some level he thinks about her. Maybe at the lowest points of your relationship he regrets not taking the chance with her when he had it. But he'd never cheat he's against cheaters and he still has love for you so he stays and doesn't stray.

OR

Your husband (future or current) meets a girl who's objectively very physically attractive. She's deeply into him so he fucks her. He had a bit of fun but honestly now that he's fucked her he could barely care if this girl got hit by a bus.

He might fuck her every now and then for a lil release but he isn't cuddling her after sex or anything he simply doesn't like her as a person, if anything he actively dislikes her for pursuing a married man and mostly just ignores her. If she ever tries to disrespect you he shuts all talk of that down.

She is literally no better than a warm whole to him. You're the only woman he reveres and whom he actively wants to provide comfort and security to. If she got pregnant he might just push her off a cliff if she didn't abort and he'd get away with it somehow.

No one would need to know about either situation so you wouldn't look like a fool to anyone.