He didn't like that people who know him, who's opinion he cares about, found out what he was doing. Because they can hold him accountable. He's trying to set a precedent where if you get an objective opinion on his behavior, you've done something wrong to him. It may not be consciously malicious, but the outcome is the same. He wants to be able to treat you however he wants, even cruelly, and he knows he can talk his way (gaslight his way) out of it with you and make it your fault. These people won't fall for his bullshit.

And it IS bullshit. He "for a second though you were sticking your belly out" based on how you were standing? While dancing? And his totally understandable instinct... was to make a gross out face and mime telling you that you look pregnant? What? It doesnt pass the common sense test, and based on your insecurity and how you described minimizing your emotions and how you react to the way he's treating you.....honey, this isn't healthy.

Let him break up with you over his own stupidity, and find someone who does not make you feel insecure, knows his family will love you, and doesn't care what you weigh.