Yes, I agree with Ms. Plath, his wanting to use you for sex and admitting it is about him, not you. I'd be glad I was well rid of him. It sounds like he's looking for someone else more attractive to him and you don't want to be attractive in his way.

I know it hurts a lot now; I did not have a prom date, did not go to the prom (though my mother got me a dress in hopes, my mother's hopes were in there too that "I" dashed by not having a date) but, again, like S.Plath says, it gets much better when you get older and in a wider set of situations. Think of when you were in 3rd grade :-) say, and what mattered to you then and why that was (because you didn't have a very large range of experiences or know many other people) I have gone to my high school reunions for years 5, 30, and 40, will have reunion #50 in 5 more years. Whether one went to prom or not is not something others remember or hold against you, and I wish I had not held it against myself.

Definitely start developing your own style, doing what you really want, regardless of external looks, weight, what others are doing, etc. If you have your own thing going, others will be attracted to that and they will be others "like" you who admire and appreciate who you are and are becoming and what you are doing. Lose weight, if you want, for you and who you are rather than because it is something you think those around you want. I was gorgeous when I was your age:

but gained weight later in life, in my 30's and on (I'm 62). I married when I was 39 and could not be happier and both my bald, fat, husband and my own 100+ lb. overweight self have that lifestyle I could not even dream about when I was your age. Develop hope and keep working for what you truly want. It hurts now but it will not always hurt and you should not let it wound you. You are attractive "enough" and on the life path you are on and have all the tools to make it a success for you. Don't worry about the shallow guys; perhaps now you can identify them better so you don't have to be hurt later in life by them. I'm reminded of the movie "Legally Blonde" :-) That movie is fun because those types of things do happen!

I love the John Masefield poem:

I have seen flowers come in stony places
And kind things done by men with ugly faces
And the gold cup won by the worst horse at the races,
So I trust too.

Learn to trust yourself.