The conflict arose because the OP’s current wife has repeatedly called the ex-wife “fat” in a negative way. When the OP asked his wife to stop this body shaming, she reacted by accusing him of still being in love with his ex-wife, leading the OP to question if his insistence on protecting his ex from insults while affirming his love for his current wife makes him the asshole.

I (45m) married my 2nd wife (29f) a few years after my ex-wife (47f) divorced me. I’m thin while current wife is on the heavier side but my ex-wife is much heavier than her. I honestly prefer a woman to be on the heavier side.
My wife has referred to my ex as “fat” multiple times, in a derogatory manner.
I asked my wife to stop body shaming my ex, and my wife accused me of still loving my ex. I love my wife but my ex is a good person and the mother of my children. I want my wife to know I love her but I don’t want to hear anyone insulting my ex.
Am I the asshole ?
Conclusion
The central conflict revolves around the OP’s desire to maintain respect for his ex-wife, who is the mother of his children, while simultaneously reassuring his current wife of his love and commitment. The OP feels caught between defending a non-present party from insults and managing his current wife’s insecurity, which manifests as an accusation that defending the ex implies lingering romantic feelings.
The core question is whether the OP was wrong (an asshole) for asking his current wife to stop insulting his ex-wife, despite the current wife interpreting this request as evidence of unresolved feelings for the ex. Should the OP prioritize protecting the ex from derogatory language, or should he have focused solely on validating his current wife’s feelings and ignoring the insults directed externally?
Here’s how people reacted:
People can be nasty in this world. I’m a heavier woman, 280lbs, 19, and chronically ill with a metabolic disorder. I used to work w a guy who would ALWAYS talk shit, saying stuff like “if you were skinny, you would be really cute and i would date you” or “when are you going to stop the bulk” and random shit like that. It was so annoying and frustrating. People can’t see past your size for whatever reason. I’ve just given up until I can find a sweet guy who respects me lmao
If she can’t handle that, well, maybe re-evaluate. Remember jealousy plays no good role in a healthy relationship.
I think you should hold the line of not tolerating disrespect towards your ex. There is no reason to be disrespectful or mean towards anyone. If she feels insecure about her place in your life, there are healthier, more secure, more collaborative and loving ways to address that.
Your wife is being immature. Her comments could be damaging to her relationship with your children if they pick up on her nasty attitude towards their mother.
On the bright side, karma will get her when she hits perimenopause though. 😂
You are right to ask him to respect the mother of your children, there is no debate.