Ki ni Kuwanai Charao ga Kite kara Isshuukan no Dekigoto

Very arguable whether this has a good ending or not, but since some people in this very thread sees karmic or vengeful endings as good ones, then they might favor this one.

At any case, it is a BSS spin, the dude never gathers the courage to confess to his childhood friend, a dude takes her away and the MC is hammered with despair all the way every chance he gets to see or hear they have sex.

However, the narrative takes a sudden turn at the end, where the MC decides to stop feeling down for a lost opportunity of scoring his childhood friend, focuses his attention on studying hard to secure a financially healthy life, and he does just that.

Meanwhile his CF got pumped and dumped, after she fought with her parents to follow the dude she thought would be her man, she got pregnant and had to shamefully come back home, to live with her parents as a single mother; apparently she wants to see the MC again but he is not interested in seeing her anymore.

https://exhentai.org/g/3608004/1e587869d2/

This turn at the end is a somewhat realistic result of a naive girl opening her legs to the first guy that looks like a masteclass lover at first glance, but they often just pump and dump, and the girl is left in shambles, specially if they have gotten pregnant, as a single mom coming from an irresponsible act their social life takes a massive hit henceforward.

Ki ni Kuwanai Charao ga Kite kara Isshuukan no Dekigoto | What Happened A Week After A Fuckboy I Dislike Came got an english translation, which is unexpected, but a welcome one. Don't know if people here will like it though since it shows the MC moving on with his life and due to its realistic ending, but I give it a read.