Some tax filing questions?

You don't have to file jointly, but it almost always means you pay less tax if you do. And no he can't "claim" you if you file separately. If you have more income this year, yes you'll pay tax on it so your refund will be lower unless too much is withheld on your new job. But if you work for Chacha, you won't make enough to change it a lot - but nothing will be withheld, so your refund will be a little lower if you make ANYthing.