I cried in front of my mother in law

She's been super nice to me. Problem being that she is so nice and the house is quiet, everyone is warm.... I don't know if anyone can relate but it's such a stark difference from my family that I don't know how to react. I burst into tears at one point and excused myself to the guest room. Like this type of evironment is comfortable, to the point where it feels very alarming.