Help me please:)

Hi I'm looking for a yaoi manga that I read a long time ago. Apparently, two boys are a fiancee (I guess/?) since they were little (it's like a promise made by their mother) but one of them thought that the other one was a girl by looking from a picture. After knowing that his partner is actually a boy, they still ended up together. I still remembered the scenes about one of the boys came and stayed up in his partner house. Well, I can't seem to remember the title and I hope some of you guys might know(=・ω・=)