http://www.mangago.zone/read-manga/mashita_no_fudanshi_kun/mf/v01/c001/16/ "sperm doesn't spurt that far" - ahh yes, the yaoi skeptic LOL
found this timeline for anyone who might be confused about the progression of the story! http://alliandoalice.tumblr.com/post/129187300952/timeline-19-days
At this point the mangaka should give them a happily ever after in the main story and jus keep writing about their sexual escapades instead