I don’t think bickering over whether a size fourteen is ‘fat’ is really helpful to the OP, she can do the maths on a BMI calculator and isn’t going to be magically persuaded she’s not overweight just because others are trying to make her feel better by saying she isn’t. Plus clothes sizing is an odd thing, in some shops I’m a whole four sizes bigger than others!
And it’s not the point anyway.
He can say he’s just being honest but he’s being cruel. There was no real need to say what he did. If he genuinely was concerned about your weight and didn’t find you attractive anymore (for example if you’ve put on a lot since you met and were first attracted to each other) there are ways to approach that! My OH and I both realised recently we’d put on a stone or two each since getting together, so we supported each other in making changes to get it off again. If he put so much on I wasn’t attracted to him anymore or vice versa you bring that up in a sensitive way first, see how the other person feels about their weight, if they’re happy with it. And if the attraction has gone but the person is happy with their weight and doesn’t want to change you can make that decision to walk away, as sad as that is, attraction is important in a relationship. To some more than others (it’d take a LOT for me to not be into OH anymore physically but some people have a narrow preference).
He said this to be cruel. If that was his genuine reason for not going he should be looking within himself as to whether it’s his problem, what he can do about it. He said it so bluntly to hurt you and knock you down and destroy your confidence when a white lie that he just didn’t fancy the trip would have sufficed.
I don’t think he likes or respects you OP, I’m sorry. I’d end this relationship if my OH said something like that to me. It’d be fine to be less attracted to me if I’ve gained significant weight, attraction can’t be helped. But it wouldn’t be fine to say something so blunt and hurtful to me about it and then pretend it’s just ‘honesty’. He tried to hurt you with those words and that’s unforgivable imo. Weight issues aside.