I don't if this is the one you're looking for but it is similar to what you've described.
http://www.mangago.me/read-manga/the_good_teacher/
Darling that's korean... What i'm search for is Japanese... But thank you soo muchh
Ohh or maybe this http://www.mangago.me/read-manga/first_come_first_served/
Ohhh it's this one!! Thank you!! (づ￣ ³￣)づ
Yw (๑•ㅂ•)و✧
I read this manga (Japanese not manhwa/hua>>>korean/chinese). Story was about a guy who got dumped by his gf because he has some problem with having sex? Cuz he's a virgin if i'm not wrong, then he goes to a bar(?) And then there he met the uke, who seems a little bit slutty, then the uke was like then have sex with me you virgin. Then they go to have sex but when they're on it the uke think that he could take the lead cuz he's not some 'virgin' like power bottom. But when they finally on it, the seme was really amazing and the uke was shocked,, and then they continue that relationship. And it's already completed.
That's all i remember,,, please if anyone might get something from my story,, and sorry my english isn't that good ╥﹏╥