Normal or a Red Flag?

My husband said that he liked to “show me off” to his “ex” and that he liked when she saw us together being affectionate. Years after we moved in together he secretly contacted her with an incognito facebook account and messaged her. After 10 years of lying about how he didn’t, he finally admitted to me. But I asked what he was trying to get out of it and he said he wanted her to see we were still together and rub it in her face again.

He claims they weren’t even a couple and that he didn’t even like her and he ended things with her.

I have never felt this way towards an ex. I’ve always just moved on from them and didn’t care what they thought of me. I’m not with my exes so why would I care what they think? Why does he care what some random girl from so long ago thinks about him and his wife?

Is this a normal thing for men? I often worry that he would have left me for her if the opportunity presented itself (like back in the day). Or maybe (more realistically) he has regrets about not dating her? It shouldn’t matter at this point but I can’t stop worrying that this is a red flag?