I can 100% understand not wanting to "relive" it, but OP's husband said that talking about it would make him feel like he's forgetting his husband. I don't think that's really the same thing. Someone else gave a more plausible explanation, but grief convinces people of all kinds of things, so ultimately, it's probably useless attempting to reason through something like this coming from someone I don't know.

I'm admittedly still not sure I understand the logic behind not telling you, but I hope the both of you are able to work things out.

I mean.

The only thing worth mentioning about the first girl was that she was hot, apparently. OP literally made a point of pointing out that this other girl is not as hot as the first girl without a single other mention of issues with the first girl or their relationship, but their attractiveness is apparently the one thing worth noting about either of them in OP's eyes, so Idk what else to assume other than it being some kind of emotional attachment to the other girl that drove him to break up with the first. Like I said, emotional cheating may very well not be the exact term, but in the moment I couldn't think of something that conveyed the issue better.

This is probably me reading too much into this, but kinda weird the only thing you thought worth mentioning about this girl you supposedly started having feelings for again is that she's hot...

You should feel like an asshole. Because what I'm getting from this is that you were most likely emotionally cheating on your first girlfriend, since you broke up with her explicitly to date someone else. Idk, maybe I'm just overreacting or just not coming up with the right phrase for it, but I don't know what else to call it.