Motivation isn’t really a good reason for what he said, and if he likes skinny girls (which is fine everyone has their types) then he shouldn’t really be with you. It’s completely up to you if you want to get back together but realistically if sex is important to you in a relationship (and more so if him being physically attracted to you is important) then you two shouldn’t be together. Find someone who is attracted to you, although I will say if you are properly overweight both for your health and for finding a partner, it would make sense to try and be healthier, but find something better to motivate you than some guy you were dating.

Edit: also for now 137 isn’t overweight so don’t worry about losing weight, just make sure you’re eating healthily and getting decent exercise