Sorry, but this guy is just an abuser of a different stripe to your last abuser.
You are attending therapy to improve your self esteem. He is threatened by this so he's trying to keep you down and in your place lest your therapeutic journey lead you to realise that you deserve better than him or better from him.
It's a dynamic that is as common as dirt.
There is simply no other explanation why a grown man would deliberately and insistently initiate conversation with their partner about how crazy attractive he finds another woman against their partner's repeatedly expressed wishes.
I mean, he's even going out of his way to message you to bring it up when you're not together.
Who does that?! Seriously, why would that even occur to him to think of, much less do?
....The thing is, it is not immediately, always disrespectful to casually mention finding a particular celeb attractive once should the topic somehow come up in conversation.
However, the vast majority of grown men in relationships have the decency, common sense (and survival instinct!) not to repeatedly go on and on waxing rhapsodical about how gorgeous/sexy/attractive another woman is. No-one with any respect or consideration for their partner does this.
...That this guy insists upon doing so despite knowing your wishes, your history, and your current therapeutic goals - that he even feels compelled to message you to initiate conversation about it when you're apart! - tells you that he has an agenda... That he is getting something out of doing so.
To wit: keeping you at a constant low-level hum of anxiety and self doubt and constantly reminding you how much more desirable he finds other women in order to elicit in you a need for his validation and/or tie your sense of self-worth to his approval.
Also a dynamic that is common as dirt. E.g. see 'negging'.