I see EnglishDave's point about independence, although I suggest seeing this family home environment as your way to save a lot of money for now. Tell yourself, I'm choosing to stay to save up $xxxx and will move out when I'm financially ready.
About motivating yourself, I really struggle with that. I have been reading about it and some people say to write your personal mission statement. Write a bunch of uplifting words that describe your life so far and choose a few that apply to all situations but fit you ("I am a caring adventurous student of life"). another thing to help is make a list of all the things you want to have, be, and do, and then choose 10 and prioritize them and then you have some good goals.