So he already got his fiance or something pregnant????

I don’t think they did it, in chapter 31, the top rejected him and said something about him getting a procedure. Dunno what it was exactly though, but tbh he was way too obsessed and stuck to the mc for him to have the time to do anything with the other guy

No he did not , artificial insemination was the method he used. I guess .
You'll learn more about Fiance's Pregnancy in future chapters.
Is he really carrying ML Child or someone else's?