A sticky situation involving sisters, money, boyfriend and a kitten?

Give your sister a couple of days. Let her think. Ask her if she'd like you to move out. Maybe she's just stressed over school. You already spent the money for a kitten so tell her you need to go through with it. Tell her you love her and you'd rather live with her. Once in awhile include your sister when your boyfriend comes over. Order a pizza , sit around and talk. Pets help people when they're stressed. I have a little dog and it's very comforting when he sits next to me. I'm sure your sister will feel the same way. Don't give up on your sister she needs you right now even if she doesn't realize it.