Is it (f27) morally appropriate to threaten my (m21) boyfriend with leaving him if he doesn't stop talking how he is depressed because his penis is supposedly "too thin"

I really cannot stand it, I wish I had power to totally forbid to mention this.

Maybe it's my fault because I let him start this debate but now he talks about it every sex night. reads about it, discuss it on the internet, and has all kind of new arguments:(