I feel like there is more to it than that, we just don't know what it is yet. Eito's reactions to Noel in other scenes and chapters seem... a bit extreme for it to just be drifting apart.
The feeling I've gotten is that Eito is aware that Uesugi likes Noel and sees her as a threat to his liking Uesugi. He seemed downright hostile to her deciding to take Uesugi to the bathroom during class break in the last chapter.
It's also possible he's aware that Noel doesn't like Uesugi and only wanted to play dress-up doll with him and feels like she'll hurt Uesugi. I don't think that would explain his reaction to her after Uesugi turned into a girl, though.
Some areas in Japan do have problems with 'pickup artists' aka annoying pushy men harassing women to hang out with them. Unsurprisingly, this does not result in lots of couples dating, just lots of women feeling uncomfortable.
I still hate this trope though.
Pickup artists definitely don't lead to more couples, they
do however tend to lead to more rapes. And that's why anyone who understands what it's like to be on the receiving end of that behavior, or are empathetic enough to be able to understand how it'd feel, hate the trope. It's very,
very rapey.
Especially when you have a situation like this one where one of the two girls is so small she needs children's clothing to fit her. Noel doesn't seem to be much larger than Uesugi either, so you've got two creepy guys hitting on what look like two little girls. Noel & Uesugi
aren't in their school uniforms either, so the guys don't know they're middle school girls based on that. (And hell, they're only in middle school, so 12 - 15.) Even by pick-up artist standards these guys are creeps.