When the man who likes me is Yandere

I'm not sure if it's a good thing for my family to remarry.
Just because my dad loves me, he said to me in a request.
On behalf of my busy parents, I came out to eat with a boy who would become my younger brother.
"by the way."
"Aren't we a family without a drop of blood?"
"Isn't just a family, but a family dating?"
What the hell have I heard?....