If you're not legally married, then you cannot claim that you are on your taxes. You may be able to claim HoH, but your (girlfriend now) would have to be completely dependent on you for support. If she works and has income of her own then this would be difficult. I recommend following up with a tax consultant for better advice on how to maximize your 2009 tax return. It sounds like you certainly have a situation where a lot of follow up questions may be necessary.
You cannot file jointly if you are not married. Unless you have a qualifying child you are not head of household either. You can file single and claim her as a deduction if she does not provide over 50 percent of her own support.
Any individual seeking legal advice for their own situation should retain their own legal counsel as this response provides information that is general in nature and not specific to any person's unique situation. Circular 230 Disclaimer - Advice given in this response cannot be used to eliminate penalties with the IRS or any other governmental agency.