Like having to confess to some loser because of a punishment. Then they turn out to be a really good couple but others in the known that it was a fake confession destroy the relationship.

Something like that. Lots of drama and regret please

Idk but you mught like it: "Last Game" by Shinobu Amano: This manga follows the story of Yanagi, a boy who excels at everything and Kujou, a girl who always comes in second place. Yanagi confesses to Kujou as a joke, but she takes it seriously and accepts. As they enter high school, their relationship becomes complicated, and feelings of regret and misunderstanding arise.
OR
"Love, Chunibyo & Other Delusions" (Chuunibyou demo Koi ga Shitai!) by Torako and Nozomi Ousaka: In this manga, Yuuta Togashi, a former "chuunibyou" (someone who believes they possess supernatural powers), starts a new high school life hoping to leave his delusional past behind. However, he encounters Rikka Takanashi, who still lives in a world of fantasy. Their relationship begins with a fake confession, but as their bond deepens, the consequences of their actions bring drama and regret.

Don’t believe in the me that believe in you, don’t believe in the you that believes in me, believe in yourself who believes in you!

Asahina Wakaba To Marumaru Na Kareshi

Rokkon Shojo
TeppenMezashiteTondeAruYo
Let justice be done, though the heavens fall