Honesty is the best policy!
Boyfreind chooses to tear down car. He has money for mechanic. Car not working for a week. He doesn't want to stay at home to work on it, but rather go dancing. I don't want to use my car gas and don't want to ride in his "old" car. How do I tell him?
Was it YOUR car?
If so ... Tell your boyfriend he either fixes it in the next two days, or he'll pay the mechanic to fix it. Then if you have to take it to the mechanic, file a small claims suit against your boyfriend.