i had an experience like this just last night!
my partner em and i went out to dinner with my ex, diane, and her boyfriend. long story short: diane and i split amicably when i moved away for work/family. we text/email very occasionally but haven't seen each other in quite a while.
when i met diane she was already a big woman - well over 400 lbs (maybe 450? i can't remember now). she gained to something like 500 lbs in the couple of years we were together. likewise, i gained from 160ish to maybe 250 lbs during that time. it was my first experience being "fat."
we broke up just as i moved and as the pandemic started. this is where our stories diverge. i continued to work through the pandemic, but i was working from home. i was also getting almost no physical activity! as a result, i piled on weight during that first year of the pandemic.
then i met my current partner, who likes fat guys. and i put on another 60 lbs over that year, and i am bigger than i ever expected, at about 400 lbs!
meanwhile, during the pandemic diane took another path. she started dating her current bf who happened to be a personal trainer. so she started to eat better and get more exercise, and started to lose weight.
yesterday i realized that the tables really had turned! we didn't talk about our weights, but it was obvious that she has lost a bunch of weight - and that i am the fat one now!
diane clearly thought this was hilarious, and commented on how it was obvious how i got so big based on what i ordered at the restaurant.