Need help finding a manga!

So I've once read this manga, about an innocent uke who's so cute and doesn't know anything about sex or even touching himself and sexual stuff. So his classmate starts teaching him about it and one time while they were jacking off, the seme found the uke so cute that he tried inserting his finger in his butt and that made the uke panicked and scared and he pushed him away cause he didn't know what was happening and so on...
Pleaaase help me find it, I've read it before but I can't find it