If roommate has been paying directly to the landlord for past year, then he is not a roommate. He's already a full tenant under the RTA, and would be implied he's covered under the standard Ontario lease agreement even though they never signed one. Verbal or implied tenancy contracts are just as valid.

This sounds like a tenancy in common meaning you each have a separate tenancy with the landlord. So your leaving should have zero effect on the roommate, he can stay and continue to pay his rent to landlord. Landlord would be responsible to find a new tenant to take your spot.

If landlord tries changing the locks on him, he could be get in trouble and face lots owed in compensation and fines.