You can not claim your dependent's deductions, like mortgage interest, on your tax returns.
You do not add your dependent's income (W-2 or otherwise) on your tax return. If it needs to be reported, he has to file his own tax return.
The question you haven't asked is: does your BF qualify as your dependent. He does not if his W-2 (box 1) is more than $4150.
A person can still be a Qualifying
relative dependent, if not a Qualifying Child, if he meets the 6 tests for
claiming a dependent:
1. Closely Related OR live
with the taxpayer ALL year
2. His/her gross taxable income for the year must be less than $4150 ($4,050 in 2016-17)
3. The taxpayer must have
provided more than 1/2 his support**. That's unlikely if you are living in his house.
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
**The IRS has a worksheet that
can be used to help with the support calculation. See: http://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf The support
value of a home is the fair market rental value, divided by the number of
occupants.
