
Could it be that? It's just a one shot tho, I tried to look up in the tags http://www.mangago.zone/read-manga/usotsuki/mf/v01/c003/

oh my gosh no way that was straight up mean.
I meant these little cuties http://www.mangago.zone/read-manga/ai_no_gebokutachi/ms/online_manga/6371-3.html
ε=ε=(ノ≧∇≦)ノ

I'm not sure if you've ever seen sex between two people who are overweight, but it isn't easy to draw without making them look comical. It has nothing to do with being gross or wrong or bad, it is just difficult to get the bodies to look proportional. Didn't you notice that Yone changed in size from one frame to the next? This mangaka tried very hard to make Yone look cute and natural with his weight and not comical. That lead to Yone looking almost like a toddler at times. Now imagine trying to get that cute and natural Yone into a sexual position without making him look like toddler-esque shota. As for Yone growing up and being thin, that happens in real life to chubby kids, especially boys. My husband and son were both Yone sized high schoolers. My son is now 6'6" and a trim 195 pounds. My husband is 6'4" and 270 pounds. Dad's still chubby. LOL If I had any complaint it would be that Yone should have been taller, but then he would have broken the typical "shorter uke" stereotype. So, in short, I don't think this mangaka drawing their intimate scene when Yone was older and thinner was a social statement as much as it was just easier to draw, particularly for their style.

It was also important that Yone changed dramatically over the course of their relationship to show that Arai didn't love Yone for his fat, he loves Yone, regardless of his weight, height, age, looks, etc. I think that was the point of the manga. Arai loved Yone for the person he was, not for the way he looked.

Try reading bara mangas...
They draw men who are huge, some with massive muscles, others with huge fat roles, all the time, so clearly drawing fat men is not that big of a challenge.
I still consider changing him from fat to thin and only showing sex after he is, to be sending a very clear message: being obese is not attractive or OK.
That's not actually a sentiment I disagree with because being overweight is very unhealthy, but the author was pushing the idea that him being fat didn't matter at all.
If that was really true, the author should have followed through and, at the very least, showed them being intimate while he was still overweight.
In my opinion, the mangaka just wasn't as comfortable with the fat factor as she wanted people to believe she was.

Well, that is your opinion and I'm not going to try to change it, but I also don't agree. My husband and I are both overweight - we're also pushing into our 50s - and sex isn't bad, but it isn't like it was when we were in our 20s either. It is awkward, not because of age, but because our bodies have a harder time fitting together with extra pounds on them. To be a bit coarse and frank, there are positions we can no longer reach because my husband's, or my, belly gets in the way. Now, imagine drawing the two of us. It would not be sex, it would be comical. Is it better that the mangaka draws the "goat fuck" of a sex scene that makes you laugh at overweight people, or the sex scene that appeals to a much broader audience? Because I can put myself into the shoes of the overweight person - since I'm no svelte model myself - I know I wouldn't want thousands of people laughing at how ridiculous fat people like me look while trying to have sex. So, to an extent, I think you're right, she chose the more appealing sex scene. Appealing, not because he was thin, but because showing sex with an overweight person would be seen as comical. It was more appealing because it was less likely to offend.
There is also the fact that most overweight young people, particularly males, tend to "grow into their baby fat" by the time they enter college. My son, at the start of high school, was the spitting image of Yone. By college, he had grown to 6'5" and a lean 190 pounds. So, based on that fact, seeing Yone later as a trim adult isn't a slight on overweight people, it is simply a fact of growing up.
Offense is rarely given as often as it is taken.

I failed to respond to your comment about bara.
Bara is essentially hentai and to that end, the bodies are drawn with ridiculous misproportions. Dicks the length of the average arm, from shoulder to wrist, and the girth of a 2 liter bottle. Something like that would make even Jonah Falcon blush with embarrassment for his small size. So, of course they fit together properly. And, I'm sorry to be the one to tell you this, but sex in bara is comical. That is the point of it. The characters in this story are not drawn this way. All the proportions are relatively correct and nothing is intentionally misproportioned for effect. Thus, comparing men in bara and this manga would be like comparing apples and trucks. Try drawing an overweight, but properly proportioned, young man with a, generous, 7 inch penis. Half of his penis is hidden under his belly. Is this a better view of overweight people? The truth is harsh and can be much more insulting and embarrassing than just skirting the issue and trying to save face for those who are overweight.
This mangaka worked hard to write and draw this character in a very realistic, yet, sensitive way. Even when he is shown pulling up his shirt and exposing his body, it happens at the crucial moment when he is being fully accepted by the person he loves and admires. Whenever Yone is shown to be ridiculed or even joked with about his weight, he is rescued and given confidence by Arai. To assume, after all the effort the mangaka took throughout the manga to make Yone the kind of character that was appealing regardless of his weight, that the mangaka then does a 180° and pushes a "perfect body image" agenda in the extra is just insulting to all her efforts. I'd rather give credit where it is due and assume that Yone was modeled after a friend or relative who was overweight in childhood and trimmed down as they grew into adulthood.

The message WAS that his weight didn't matter. He didn't care if he was skinny or fat, he just loves him. That's the message.
Another reason could be that people were just assuming Arai has a fat fetish so they wanted to show him loving him when he's skinny too to prove them wrong. idk about that theory tho.
Regardless, the manga still shows that it's okay to be fat and that even if you are, someone can still love you.

Then why not show the 1st time they had sex when he was still chubby?
It's not like there is a limit on how many sex scenes a story can include.
Honestly, in yaoi mangas the rule is typically the more nookie the better.
In this case, however, the option to show one sex scene (skinny) but omit another one (fat) just came across as reinforcing the idea that fat is unattractive.

Well one possibility could just be that they had difficulty drawing him. I know I for one have a harder time drawing people that are chubbier, just can't seem to get certain positions to look right idk. Another reason could be that they hadn't planned on extending the manga that far. They could have had fans asking for a continuum so they just threw it in for the people that were curious about what he'd look like skinny and for the people that were upset that they couldn't see them have sex. I mean I'm not trying to give excuses for the mangaka, I just don't like when people immediately jump to their own accusations before thinking of other possibilities.

It's like you can't do much of anything nowadays without people misunderstanding and taking offense when no one meant to offend them. Can't praise thick girls without the skinny ones getting offended, can't praise the skinny ones without the thick ones getting offended. It's like people are creating judgments so they can take offense to them it's weird. Sorry that didn't really have much to do with this. I just thought of it and decided to share it, you can just ignore it ╮( ̄▽ ̄)╭

I wish everyone would just refrain from judging others and also refrain from automatically assuming people are judging them. The human race is just doomed I swear. We create our own problems. We're all hypocrites too, no matter how you look at it. Why am I getting all philosophical in a random comment thread...
I love it, but I wish it was showed a bit of them having sex while Yone-chan was still chubby