No. He also cannot file as Head of Household.
You and your son may be his tax dependents, so he can claim your $4000 exemption (deduction), if you lived with him all year (see full rules below). But because you and your son are not related, your cannot be a qualifying child for the earned income credit and child tax credit and neither of you are a qualifying person for Head of Household filing status.
A person can still be an other dependent (Qualifying relative in IRS parlance, even though they do not have to actually be related), if not a Qualifying Child, if he meets the 6 tests for claiming a dependent:
1. Closely Related OR live with you ALL year
2. His/her gross taxable income for the year must be less than $4,000 (2015)
3. You must have provided more than 1/2 his support
4. He must be a US citizen or resident of the US, Canada or Mexico
5. He must not file a joint return with his spouse or be claiming a dependent of his own
6. He must not be the qualifying child of another taxpayer
You may be able to file as Married Filing Jointly if you live in a state that recognizes common law marriage. Currently, the following jurisdictions recognize common law marriage:
District of Columbia
Georgia(1997), Idaho(1996), Ohio(Oct. 1991), and Pennsylvania(2005) are grandfathered for the marriages before the year indicated. Living together in a common law state is usually insufficient - you need to hold yourself out as married including owning property together, having joint bank accounts, etc. To find out your state’s rules see:
If you are able to file jointly, then you (the couple) DO have a qualifying child for the tax credits.