The Angelic PE Treatment Clinic - Version 3 by Bear Fruits (Eng) - Adult Sex Game

The protagonist has a rather embarrassing problem: because he has premature ejaculation and is a total masochist, he loses without fail to every monster girl he encounters in dungeons.
But one day, he happens to stumble upon a sign that reads, "The Angel Clinic: Specialist in Premature Ejaculation Treatment"...