I have financially supported my 25 year old roommate for the majority of this year- with housing, food, utilities, etc. He has had no income, and has paid nothing to me this year. Can I claim him as a dependent to write off those expenses?

In general, to be claimed as a dependent a non-family member must have lived with you the entire year, have less than $4,200 in gross income, and you must have provided over one half of the total support for the dependent in the year. There are other requirements for the dependent such as not filing a joint tax return, not being claimed as a dependent by someone else, and must be a US citizen with a Social Security Number.