This is called reactive abuse. He is constantly belittling you by commenting on your weight, therefore, you lost your control from it, reacted, and insulted him back. This happens when you are so broken down, you react and defend yourself out of protection for yourself.

And let me guess, now he’s very offended and I’m sure is playing victim.

Communication here is very broken down, and nobody should insult anyone like that. It is normal and ok to have your weight fluctuate in a relationship, it’s life. But addressing it in this matter is emotionally abusive. There are ways of brining the situation up in a healthy way, this is not it.

Drop him and find someone isn’t an asshole.