I don't think you're dumb, and I'm not sure how long you've been reading, if it's from the beginning (like last year), this story has gone on for so long and it can be hard to remember, i even had to re-read when i write. but essentially, to give yoongi and his career the chance jimin believed he deserved. yoon's career was and still is so important to him and jimin believed that having a child at the height of it, when the company had already so clearly said they couldn't be together, would have ruined what he worked for.