Husband says I’m too fat and he’ll cheat on my if I don’t lose weight

Me and my husband have been together for almost 8 years and married for 5. It’s always been great but recently he’s started saying I’m too fat. I started gaining weight during Covid lockdown when the gyms in my area shut down and I went from 5’5 110 lbs to 123 lbs. Yes I’ve gained weight but I didn’t realize how bad it was. He’s always been so nice to me but now he calls me “piggy” and chubby and says “since when did I marry a pig” when I eat.

That was fine with me but now he’s saying that he wants to cheat on me with fitter women and that he will unless I go to them gym and start losing the weight I put on. To be clear I already go to the gym but it’s more to build muscle than to lose weight as I didn’t realize I was that big. I haven’t seen him in a few days after he kicked me out our apartment and I’ve been staying with my parents. He says he hasn’t slept with anyone else yet but he will this week if I don’t agree to lose weight. I will start to lose weight to win him back if I have to but I’m just trying to think of ideas to win him back without having to lose the weight. Anyone have any tips as to what I could do to make him happy with me without losing weight?