You said....
'Um, I feel fat and I have historically had no problem going to bed with men because I am quite sexy without trying (I don't think so but I have been told I am and that I need to work on this if I want more than sex) but I have a shitty history as far as relationships go.'
and that worries me.
Every woman has 'fat days' and that really is about self confidence. Not many people think that they have the perfect body, so the rest of us just have to deal with it the best way possible, and that is a lot to do with self confidence.
And, not to shatter your illusions, but pretty much any woman on the planet could walk into a bar and find a man willing to have sex with her. That's just the way it works. Its finding a guy who is worthy of you and the right guy for you that is the hard bit.
If you want to change how people see you, then think about the way you dress and carry yourself and what you speak about. These are the things that people make a decision about you based on. And they are also the things that you can control.
And eveyone has shitty relationships. But they are in the past, its now that counts. Don't push this guy away and prove yourself right!!!!