That sounds really interesting!
Based on the storyline you described, I'd recommend:
"Mizutama Honey Boy by Mayu Sakai": This manga follows the story of Nao Kogure, a high school girl who harbors a crush on Taiga Onise, a fellow classmate known for his intimidating demeanor. Nao, desperate to get closer to Taiga, concocts a plan to pretend to be his girlfriend. However, when Taiga discovers Nao's feelings and agrees to "date" her, their relationship becomes more complicated. As they navigate their fake relationship, secrets are revealed, leading to misunderstandings and unexpected developments. While not an exact match to the novel you read, it shares themes of deception, misunderstandings, and romance.
Thankkkyouuu (ʃƪ＾3＾）
I read a novel today and I was thinking maybe there was a similar manga....
Please recommend (•ө•)♡
"The girl was obsessed to the boy so she pretended being pregnant, just to get married to the man, and the man didn't know, so the man married the girl and taking Care of him. One day while he hugged his wife he saw the belly falls in the girl, so after that, the man thought the girl just lock her into the marriage , and after that the man left the girl, but this time the girl was really pregnant...."
(Don't mind my grammar ( ꈍᴗꈍ)....)