Divorce parents help?

My parents are divorced and have joint custody of me. they switch off every other week. It is currently my mother's week and her boyfriend just moved in with her. My dad just found out about the guy through ME and now he is furious. I overheard him saying "I have the right to keep the kids here if I don't trust this guy", but I trust him a lot. He is a very nice guy and so far he has a great impression on me. I want to know what are the laws on this, and what are my rights? Is it considered abduction if my father keeps me on my mom's week, even though it is against the agreed custody arrangement? Can I choose one house over another? By the way, I'm a 16 year old guy.