Aside from the mental health stuff, you need to tell your bank what happened. this is harsh but absolutely FUCK that family member. Cut off all ties with them, because they will NEVER make your life easy. They are not someone you need in your circle right now.
Whatever that check was for, figure out a way to make sure you get direct possession of your money at all times and that it's in a safe spot (not under your mattress either. a bank account that only you know about)