Confidence and self-esteem are nothing to do with actual size/shape/appearance.
I'm bi and a size 18 with a c-section scar, stomach apron, stretch marks, surgery scars, moles... My ex called me a fat pig at size 12.
The sexiest PEOPLE are those with confidence, a fun open minded attitude and who like ensuring their partner/s are having a good time too.
Most of the usual erotic products retailers have plus size ranges that tend to start at size 16, lovehoney and Ann summers tend toward the more tame/vanilla side of tastes there are others that tend to more niche tastes.
Corsets look fabulous on us larger ladies, I found my first on Amazon! but you'll find plenty other styles looking around online.
I'm in a relationship now but have dated, had fb/friends with benefits etc and here's the weird thing. My confidence grew at the same time as I was getting bigger. Not a deliberate thing pure happenstance. I've been to 'special' parties and I can assure you I didn't and don't go short of attention.
Even on a 'normal' night out I get asked out and offered drinks etc.
Even in objective (well as objective as these things can be) studies, women with larger butts, bigger hips, bigger breasts are just as likely to attract a mate.
The very slim androgynous looking figures presented in fashion media is not what everyone is attracted to.
And I'm not dissing those body types either, my own friend circle AND the women I've dated/experienced are of all different body types. And everyone in my opinion has something about them which if I don't find them attractive then any number of other people find attractive. Just as different personalities are drawn to each other.
Try this (worked for me) stand naked in front of a long mirror (yes I know very difficult at first it gets easier) but DON'T focus on what you don't like, focus on what you DO like.
Try and find at least 5 things.
I have big brown eyes, full lips, decent boobs, great legs and a very round symmetrical bum.
The more you focus on the positive the less you focus on the negative.
That said your partner may genuinely love the things you see as negatives. Mine has a thing for round bellies like almost a fetish.
You've said yours loves your bum. Enjoy that.
When you're having sex instead of worrying about what you perceive as your negatives, focus on what you love about your partner. Focus on enjoying the experience. Try new things.
Porn is hated on mn for good reasons but one thing it does show is that men LOVE all different body types. Some like plastic Hollywood barbie dolls, some like natural slim ladies, some like curvier ladies, some like very big ladies.
Even my male friends, my brother likes hour glass figures, his best mate won't even look at someone smaller than size 20, another loves ladies with lots of tattoos and piercings, another likes very prim & proper types...
Do you fancy every guy? I'm assuming your straight apologies if I'm wrong. What kinda guy is your type? My friends like all different kinds of guys too, slim, big, muscular, small, short, tall, bald, long hair, nerdy, alternative, traditional...
Seriously focus on your positives which I am sure are numerous. Inc that you obviously care a great deal for your partner. Who I'm guessing as you've been together a long time doesn't look exactly as he did when you met him either. 