I suppose that depends on a number of factors... Who is the person who sets "standards" of beauty? Would society consider me stupid/not stylish enough should I go against the views of the majority? What do you refer to as "fat"?
Over here most young people seem to be totally obsessed with beauty - and what passes for beauty is being slim. When I open the browser (the most "common" one in the Czech Rep includes some weather info, some news and some gossip-like headlines), virtually every day brings articles of the "if you have obese friends, you are likely to become fat yourself pretty soon", "xy has put on weight, look at her thunder thighs she should lose immediately", or "is there any hope for him/her (plus a photo of a fat person) to live a normal life" nature. Frankly, it is bloody frustrating. Few years back, one TV company broadcasted their own version of "You Are What You Eat", and they hired a doctor and paid her to be extra nasty towards people wishing to lose weight - basically to shame them and make them into a laughing stock. The most horrible approach EVER. Young women larger than size 8 (10 if they are really tall) are considered disgusting by a great majority of people, and are often told they are pigs fit for slaughter. When it comes to sex, plenty of young men say that a woman heavier than 140 pounds (often even less) is a hippo whose c**t couldn't even be found under all the flab. I have been trying to find a boyfriend through dating sites and I am often told by guys there that I should realize I am too fat to find anyone who isn't a barely literate drunk. Yeah, that's a really fabulous thing to say to a woman who's currently working on yet another uni degree while doing some tutoring, proofreading and translating stuff. Smashing.
People tell me things like "if you started to excercise a bit, you would look much better, and you migt even have a chance of finding yourself a date"... Well, that means they really know me and really care for me; I used to be 300 pounds several years ago (size 26 or so) and I have made it to something between 180 and 190 pounds (size 14-16) through rigorous excercise (I walk 10 plus miles almost every day, plus I do at least two hours of cycling/spinning a day, and perhaps two to three weightlifting sessions a week). I have the resting heart rate of about 48 bpm, and model blood pressure and everything. Yet I have flabby stomach and thick thighs (and at the same times I sport prominent clavicles, lean, lightly muscled arms and lower legs, and I don't even have a hint of a double chin), and cruel people (usually young women who want to make themselves look more beautiful by comparison through making others feel fat and ugly) love to point theiir fingers and me, a-shouting: "Fatso!"
That's "fashionable" behaviour, being "cool", and having bags of "style", I guess. I do appreciate that my lower belly doesn't look good (I feel like a chubby Shar Pei dog pup), and I have been seriously thinking about having a tummy tuck done - I am just slightly worried that the result might not be all that great, either. Even when I am not very happy with this fad that claims that ONLY slim, beautiful people are healthy (and that every fat creature is sick and is going to be dead by the age of 50 - incidentally, most of my blood relatives are/were also... circumferencially challenged, for example my grandpa had managed to put extra pounds on even when he had been doing some forced labour in a factory in Vienna during the WW2 (while it wasn't anything like a concentration camp, of course, and the workers could roam free when they were having their time off, Nazis didn't bother to feed particularly great and abundant food to Czech workers), he had been overweight all his life - and he died at the tender age of 88... and there would be more examples, both among my mum's and among my dad's relatives. Yet these days, wherever I myself go, I am just "not enough" - or rather, there is "too much of me". It's not easy and it's not pleasant.
I suppose I will have to learn to live with it - even though it may be nasty to evaluate others on the base of their height, weight and body shape, people just tend to do it. People are not perfect physically (and it's so easy to point out any blemishes of this sort) but, more importantly, people are no angels, they are not perfectly nice, pleasant, or fair - and since these particular blemishes, these character flaws, are not tangible, and can be either hidden under the lovely outter shell, or, on the other hand, emphasized through slandering and nasty rumous, one has to accept that people often prefer to choose their friends (and partners) because of the more easily "visible" qualities they might sport - by their physical features...
Various physical qualities get praised or laughed at in various eras and various societies; I suppose that in the late 19th century I would have been considered (yeah, despite the flabby tummy) a trophy wife by any well-to-do farmer in any part of Western or Central Europe - I have an okay face, I am physically strong, and I think I intelligent enough to be a help in managing financial affairs and perhaps even to help one or two of the kids to pursue higher education that might be handy in the rapidly developing and changing world. These days, it is different. I am a city person, a university student/graduate/employee, and I live in the world where most men don't look for sturdy big bones in a women but rather for slender, lithe limbs and flat belly that looks great in swimwear and cocktail dress; many a man wants to show his peers that he is cool, classy and well-to-do enough to afford to have a beautiful girl with fashion model qualities in his bed... The answer to the "what is important?" question keeps on changing all the time, and with it, the standards of beauty.
I know I have no chance whatsoever to pique the interest of any "stylish, charismatic, cool guy", such a man would never consider me attractive enough. But even though all the magazines and reality shows and whatever else tells us that you have to be cool and beautiful (and that you should look and act like beatiful actresses and handsome actors of sitcoms aimed at youngish adults), not everyone can (or for that matter, wants to) be that attractive and wonderful - I myself hope that somewhere in this category of "less interesting", perhaps a tad introverted, and not exactly beautiful (and slim) people there may be someone who would have me. The chance is slim (unlike myself, lol) but perhaps there is a little hope...
You seem to have been lucky already, having found a guy who doesn't feel the need to join the glamorous club where only the coolest and sexiest people (according to the Hollywood-ish standards, anyway) tend to be welcome. Your fiancé does apparently find you beautiful, having his own criteria for beauty - this is what matters, don't care about what others say.