Since Randal adopted you, being your other guy in the house (aside from Sebastian), he didn't have any guy clothes other than Sebastian's. Dal wanted you to have a different role from Sebastian, so he came up with the wonderful idea of putting you in the suit he wore when he danced with his human-sized doll

He does morbid things when you are his doll (like painting your face like a doll, bite your arm, slightly torture you, and these kind of things would he usually do), even though you are a human being... with the passage of time you and him contracted a very deep bond of friendship

right now you are fulfilling your role as Randal's human doll