Honestly I get Rihito being concerned about her (and himself) and all but I think in the end he's just shooting himself in the foot, since now his alone time's reduced in exchange for basically nothing, since Reni's still stalking Noa (who's still tweeting anyway).
I feel like he's getting more and more tired of this, although I think in the moment he'd realize any outburst would probably only make Noa worse... Sigh, good luck out there Rihito...
Well, like I said before...
He is doing all this because he wants to, he said himself more than once.
Other people cut ties with Noa before (because of her behavior), he didn't. He knows Noa is not someone that would stalk him, be aggressive with him or blackmail him with things like "I will kill myself", she will just be sad and follow her life like all her previous interactions.
Noa have a lot of issues but in the end she would accept if he didn't want to be her friend anymore, sure, she would cry a lot, but it will be just that.