She and Eito had always gone along badly because of them wanting MC, apparently.
Are you serious...? Eito just appeared randomly, maybe to say hi, or maybe he was just going to take a walk at that moment, and Noelle glared at him as if he were a shit stain like thinking "Im spending time with my Kei, fuck off, asshole", are you surprised he desired to stay and go with them after that?
Especially as it wouldn't surprise me if Kei and Eito had already agreed to hang out at least for a while.
Besides, one thing is respecting other people feelings, other to ignore your own. Eito likes Kei, and Kei also likes him, this chapter made it obvious.
It's just a question of who Kei likes more, Eito or Noelle?