Since our lists got nuked im trying to find this one. The BL was about a hero and villain dating, very fluffy and cute. I think the reason they were together was to keep the peace between their two opposing sides. They have a child together ( not omegaverse or mpreg) via magic and raise the child together. The villain had black hair, so did the baby. I think the baby kept calling the hero "hero" instead of dad/papa, too.
I believe you're looking for this manga
https://www.mangago.me/read-manga/satan_on_parental_leave_and_his_fake_hero/
There was this one manhua or webtoon, it was about this guy interviewing a serial killer? But he slowly starts to fall in love with him. I remember the serial killer being blonde.
http://www.mangago.me/read-manga/criminal_interview/ This one (〜 ̄△ ̄)〜?
“I understand but I don’t think I can forgive you.”
PERIOD