Rain's Favorite

So I"m looking for that particular BL where the seme has HUGE cock but he was very insecure of it because his past lovers were SHOOK to the core everytime he whipped it out then he found his uke who has the perfect ass and actually was hungry for a big fat cock. It's a super smut manga and I can't find it. Tried to ask the bitch Map but that piece of shitty paper is useless for the second time around