You live in your mom's house rent-free, so she wants you to live by house rules. You can't do housework because of back injuries from a car wreck (but sex is apparently strain-free

). You have already totalled at least one car ("If this last accident...." indicates plural accidents) and don't know how you're going to pay for the new insurance expense, etc.
So you should ask yourself some more questions before you decide.
1) who's going to clean the new house?
2) when you have a house of your own, are you going to have expectations of the people who live there with you?
3) if you can't make it financially now, how will you make it if your expenses are trebled?
4) do you really want to take "how to live on your own" lessons from your boyfriend? Didn't he just move back with his parents?
There will be good rent deals later, too. Think long and hard about whether this is the right time for you. There are a lot more factors in this decision than just cutting the apron strings from your mom.