@tsarstepan,
Just opinions, now, butthe roommate has been there only 3 years, so I doubt either squatters rights or prescriptive rights would apply. If rent has been paid, the roommate would have the rights as a tenant and probably need a thirty day eviction notice. The notice should be served by certified maile or professional process server, or what ever is required by the state. It shouldn't be done verbally, or by someone involved.
Again, those are only opinions.