By the way, it's possible to have a BMI of 30 and be perfectly healthy. I'm a guy with a BMI of about that, and I'm certainly not obese. Carrying a little bit extra, sure, but not obese or noticeably "fat". I'm 6'0", naturally heavily muscled, naturally enormous frame (shoulders, barrel chest) and when I was 14 years old and a county sprinter I weighed nearly 15.5 stone. There wasn't an ounce of fat on me at that point.
The lesson from this is that BMI is utter bollocks. Everyone's different. On paper I shouldn't be able to walk round the block without wheezing my last; actually I cycle 20 miles to work and back every day and I can lift any adult you care to mention of his or her feet and onto my shoulders without even really noticing the weight. I could be in more Jackmanesque shape and wouldn't mind shedding a love handle or two, but there's no belly and my chin is firmly in the singular.
However, I have been fat. Not Johnny Vegas fat, but fat enough to feel really unattractive. But even at my biggest, my weight and BMI on paper would've suggested the fucking Hindenburg, a real monster Channel 4 documentary of a person. I was chubby, but nowhere near as WHAT THE FUCK IS THAT?! as the numbers might suggest.
However, my marriage did end because of weight. I stopped finding my ex attractive not because she was fat but because she was ashamed of her body, no matter what I said and did to the contrary. But as much as she claimed to hate being overweight, she wouldn't sort out her diet or exercise, and wouldn't listen to expert advice. And then she'd complain that she was so gross and felt so unsexy, and when you have literally years of someone telling you that they're horrible and unattractive but not doing anything to change the situation, it's pretty hard to keep up with the pep talks. Eventually I did stop finding her attractive, but much more at the mental and emotional level than the physical. And that was that. We disconnected because she didn't want sex because it made her shy, but she wouldn't or couldn't address the cause of the shyness, and so over time we just fell apart.
Physical attractiveness - however you define that - is important: your partner does actually need to fancy you. And if you're with someone who's a genuine saint and doesn't care what you look like and would jump your bones even if you looked like the bloke who lives under the Chiswick flyover and shouts at the cars, then lucky you. But most of us, men and women alike, aren't like that. If our partners change physically to the point where they're not remotely like the person we originally wanted to shag, I don't think it makes you an awful person if you stop fancying them.
Sorry. Essay.