I have a roommate.
He has a job. He makes decent money.
He files his own taxes.
It's a long story, but the important things to note -
He does not pay rent or contribute to bills at all.
He feeds himself but otherwise had full run if the entire house.
He has his own bedroom.
He uses the kitchen, had his own bathroom. He uses every room of the house regularly except my kids room and my bedroom.
I own my house.
I am married and have a kid.
Can I claim him as a dependent? I pay all the bills, mortgage, etc. Are there any deductions I can take? Etc. I'm mostly lost in what I can do on my taxes here.
No. If your roommate has over $4300 of income in 2020 you cannot claim him as a dependent. There is no remedy on your tax return for letting a free loader live with you.
CREDIT FOR OTHER DEPENDENTS
Q. Can I claim him as a dependent?
A. No, because he makes decent money and files his own taxes. Supporting a person is only one of several dependent tests.
Q. I pay all the bills, mortgage, etc. Are there any deductions I can take?
A. There are no deductions you can take related to you allowing someone to live with you, rent free. As a home owner, you are allowed to deduct mortgage and property tax. These are itemized deductions. You can't (actually "shouldn't") deduct itemized deductions unless it's more than your standard deduction ($24,800 Married filing jointly)
Taxes are complicated. You almost certainly can't claim that person as a dependent.
But there's one far fetched possibility. If he's closely related (sibling, nephew), under 24, younger than you and a full time student, usually on scholarship or VA benefits. Even then, you would have to show he paid for less than half his own support.
Probably not. You can claim a non-relative as a dependent if they meet all the requirements under the Qualifying Relative rules. However, the main requirements are that they lived in your home for the entire year and that they did not have gross income for the year of $4,050 or more.
Based on your earlier statement that he "makes decent money", he probably won't qualify.
Also see: Rules for claiming a dependent