You can claim an unrelated person as a dependent under the Qualifying Relative rule if ALL of the following conditions are met:
1. The person is a US citizen or resident of the US, Canada or Mexico.
2. The person is not the Qualifying Child of another taxpayer.
3. The person does not file a joint return with another taxpayer.
4. The person lived in your home for the entire tax year.
5. The person had less than the personal exemption amount ($3,800 for 2012, $3,900 for 2013) in gross income (excluding only non-taxable Social Security) for the entire year. Gross income includes all income from all sources before any deductions whatsoever, including normal business expense deductions. If the source of his disability is anything but Social Security you cannot claim him.
6. The person received more than 50% of their total support from you for the entire year. Even with your higher income, this test may not be met once the fair rental value of his condo is factored in. If it would rent for $2,000 a month, you don't provide more than half of his total support.
7. There is no state law or local law or ordinance that prohibits cohabitation. Any such law or ordinance, even if unenforced, kills the exemption. Mississippi, Virginia, West Virginia, Florida, North Dakota and Michigan still have laws that prohibit cohabitation as do a number of cities, towns and counties throughout the country.
If you can claim the person, you only get the exemption. No Head of Household filing status, no EIC, no Child Tax Credit, etc. You definitely would not get a "ton of money." Your tax savings would be around $585 or less.
See IRS Pub 501 http://www.irs.gov/pub/irs-pdf/p501.pdf for more information.
Edit: Your marital status on Dec 31 determines your marital status for the entire year. Therefore if you marry on or before Dec 31, 2013, you would be considered married for all of 2013 and would almost certainly file a joint return which would save the most tax by far. You would not claim him as a dependent as a spouse is NEVER a dependent.
Again, the source of his disability income is critical if you are not married by Dec 31, 2013. The law is very specific. ONLY non-taxable Social Security counts. Anything else -- SSI, private disability insurance, welfare, state disability insurance, etc. -- disqualifies him as a dependent.
See the support worksheet in IRS Pub 501 (linked above) to see if the support test is met. I believe that it's now on page 15. Don't forget the fair rental value of his home! The IRS audits these claims fairly frequently, so have that worksheet completed and receipts on hand to back up your numbers.