The uke tasted the seme's semen, the seme said he shouldnt have tasted it because it has an aphrodisiac
It is part of a onshot series might be on MRM. Look up inchubuss(thats how it is spelled right?)
http://www.mangago.me/read-manga/kimi_no_nioi_ga_suki/mi/ee77140053c4b96ad12654d2e050e811_chapter-4/1/
The scene you are searching for is in the next chapter btw
The uke tasted the seme's semen, the seme said he shouldnt have tasted it because it has an aphrodisiac