HELPMEEEE

I'm looking for this manga/manwha. It's black and white vertical format. The couple has age gap (around 8-10 years) The top is younger and the bottom is in his 30's, he looks young tho. They live like a married couple (not actually married i think). From what i remember, they decide to go through an abstinence period. They're intimate with each other but force themselves to not have penetration
There's like a younger brother??? that appears out of nowhere and stays with them on their house for a couple days/weeks and they can't have sex until he finally leaves

Pls help me find it i can't remember the title and since the lists are gone there's no way i can look for it