it’s my cousin, but사촌 means “cousin,” and -인데 connects this statement to what follows, often with a contrast or explanatory nuance. Depending on context, it can also mean “he/she is my cousin.”
KO: 저 사람은 제 사촌인데, 미국에서 왔어요.
EN: That person is my cousin, and they came from the United States.