You were there first.
Tell him, in no uncertain terms, that you will not tolerate anyone dealing drugs out of
your home.
Tell him to either stop now or get the fuck out. There's no way he has a right to move into your place and compromise your safety and welfare.
Question, though (two parter) - Do you smoke weed, and, if so, is this guy giving you freebies? If so, righteous indignation might not be the way to go.
Then again, I would imagine you could always find someone willing to pay $225 for two large baggies of weed
Seriously, though - good luck. Let us know what happens.