OK. This may or may not help. Your ex is super tiny, out of the norm, especially for moms who aren't in their 20's.
So, tell me more about this woman...… tell me what she really did look like.
You need to put yourself into a mindset that you've only been with thin and toned. Do you know what it is like to feel a curvy woman? Is it an experience you have ever had?
I take good care of myself. I go to the gym, I eat good half of the time. But I fall into the curvy/athletic category. I am not thin. I am not fat. My body time I guess says " I like to exercise, but I also like beer, wine, and good food"
Enjoying the good things in life doesn't mean someone doesn't take care of themselves. That's why I find "dad bod" so hot. Some nice strong arms, a little bit of a belly, and I can tell it's someone who takes care of themselves, but still enjoys the good things in life. My current man is obessing over his dad bod and is going for some sort of perfection. I told him why I love the dad bod so much and he never really thought woman thought that way. I told him a woman who enjoys herself does!
I have met think people who don't take care of themselves. Just genetics. I have met bigger people who are in the gym every day.
FF was a bigger guy, he was my first too. But he was a cutie, we could grab a beer and burger, and go to the gym. I liked it.
If you are really unattracted, don't go on. But if it's because she doesn't fit some particulars of your type, I would say open up your horizons! Go outside of the box, just a little, one step at a time.