My advice is to use your head and play the game. Tell your understanding boyfriend to not call you on the house phone and when your mom is around, then plan your next steps. Do you want to be a JW or do you just want to avoid DFs? If so, give yourself some time to figure out your escape route.
Number one, I never let anyone hold the cards on me. Ever. It's a life lesson, control when you leave by being smart. JWs are the best actors/liars/manipulators to get the desired outcome they want, learn from your own experience and use it to your advantage.
Tell mom, you are sorry for upsetting her and whatever else you need to say to appease her at the time. Avoid lying, just talk around it. Then keep the relationship out of house and off the conversation, then figure out where you can move, save your money and look for a job. You are about to graduate college, do you have any jobs lined up? You should and if you don't, now is the time to meet with your advisors, job counselors at school (I am sure your school has something like this) and line things up.
Now, honestly, I would suggest graduating, having a job lined up, a place to stay, and then figuring out the next steps with your boyfriend/fiancee. As for the JW thing, that's your path, but if you are here on this site and want to avoid the DFs, do the slow fade, move on with your life and use your head.
I hope that helps.