Helllpppp!!!

there are two boys sharing a room. they draw a line in the center and had an agreement that they shouldn't cross that. At night, the other one always brings women to have sex and while doing it, he always say the name of the other boy or something synonymous to his name. while the other boy always used headphones for him not to hear the deeds of the other one....that's all I can remember...huhuhu...btw it's a yaoi manga