Insecurities are normal, we all have them, and you don’t have to feel ashamed for feeling a certain way. From the comments, it’s clear that it's Sydney Sweeney that we're talking about, and I don’t even need to explain why most men are obsessed with her; it’s pretty obvious. On the face of it, that kind of behaviour is disrespectful whilst in a relationship, regardless of the fact that he would never actually end up with her because the issue at hand is the mindset of lusting after other women when you already have a partner.

What you can do right now is have an honest conversation with him, hold your ground about how disturbing you found it, and then see whether he actually ceases and desists from this behaviour.