I read it once a long time ago and i'm trying to find it again. Here's what I recall.

Yandere stalker female, small, is stalking the boy she likes heavily. When she gets permission to text him she floods his phone and he has to limit her to one text a day. She makes him lunches daily. Eventually she moves in next door and watches everything he does for months through a window and writes it all down in journals. She attacks his childhood friend and kisses her because she was taking back his first kiss. In the end she moves in with him and the manga closes with their daughter stalking someone.

Driving me crazy.

Thank you and your beautiful self.