I also have a boyfriend who, while he understands why I'm doing it and encourages me, would never fast with me in a million years. He thinks it's "weird". I've personally decided not to see him this coming weekend (we are long distance see each other only on the weekends) so that I could fast in peace. I have no problems during the week, because I don't have food in my house!
A good excuse to get away from the well-meaning but non-understanding family? Just say that you're sick! Puking sick. I know that's gross, but hey, it'll prevent your parents from jumping down your throat. Tell 'em you caught a 24 hour bug. If they come over to see you, you can hide your lemonade in a Gatorade bottle. Good luck with the deception!