Its been like 3 months of time in this timeline I think, and, believe it or not, teenagers are not at peak fertility. Also, he may be blasting loads like a Blastoise, but the swimmers are mostly in the first salvo.
I have come to terms with the fact that this webtoon will never come back unless the MC loses interest in all women and starts getting flavor-blasted by every dude in school, because that's just where the author's brain is right now (stewed in cum). We lost it all to gay sex...