As has already been said, it’s not really about weight.
I had a girlfriend for nine years who would fluctuate between an 8 and 14 and was constantly in a cycle of gaining and losing weight and struggling to keep it constant. Her weight didn’t matter to me. I was literally climbing the walls with lust, no matter which part of the weight loss/gain cycle she was in, because she was so damned sexy. She always wore nice clothes, always did her nails and makeup and had a substantial wardrobe of sexy lingerie, skimpy nighties and naughty dressing up costumes… and the confidence and sexy mindset to pull it off. She dressed and acted in a way that made it obvious that advances on my part would be welcome and did her fair share of initiating too. Her mindset, playfulness and confidence supercharged my desire for her no matter what her weight was at any given moment. I still lusted after her as much in the final months of our relationship as I did in the first months.
On the other hand, I had a long term relationship with someone who constantly maintained a size 6/8 physique and looks like a Victoria’s Secret model. Things couldn’t be more different though. Initially it was like my other relationship… the lingerie, tiny nighties and dressing up, but then it all stopped. It was literally like a switch turned in her brain and “the sexy” was gone. Big, baggy knickers and pyjamas that looked like something you’d wear camping up Mt Everest. And it’s all well and good saying a woman should be enough without sexy attire, but bear in mind that visual stimulation is to men what romance is to women. Saying she should be enough without having to dress up is like saying I should be enough without having to be romantic and thoughtful.
I could have sex if I initiated it but she never bothered and I didn’t because it’s a complete turn off sensing a complete absence of desire from the woman’s side. I’d rather just do without… and did, for years. The sex, when it did happen, would be zero effort on her part - she literally just wanted something hard inside her that she could grip onto while using her vibrator to get herself over the line. No build-up, no kissing, no cuddling, no foreplay, wouldn’t let me stimulate her with my fingers or tongue… just a cold, efficient box ticking exercise and a complete turn off for me. Ironically, men are blamed for using extreme porn and then losing interest in “vanilla” sex with their partner but I was the opposite… I turned to porn to seek out videos of the soft-focus, romantic, sensual, tender lovemaking experience that I was craving for myself and that I was led to believe was what women wanted.
So, from a man’s perspective or, at least, mine, why does a man lose interest? For me it’s when she loses the “sexy” mindset. I get that you mostly want comfortable underwear and nightwear but if you never wear anything sexy at all or maintain “the sexy”, at least some of the time, it sends a message about where your head’s at and knowing your head’s in that place is incompatible with me wanting to make advances on someone. Weight would only be an issue of you were really overweight and it was due to lack of exercise and eating crap, which would be a mindset thing again. It’s all about where your mind’s at.