Sorry to hear about the abrupt turn in your rental situation.
As explained by the Tenant Resource & Advisory Centre, a roommate who rents from a tenant who lives in the rental unit is not legally protected by the Residential Tenancy Act.
What matters is what the two of you agreed to. An oral agreement is a valid contract. But if you never discussed what happens if one of you wants out of it, then the legal principle of reasonable notice applies. That is, each party must give the other reasonable notice to end the contract. How much notice is “reasonable”? Ideally, as this template roommate agreement explains, that’s something both sides should agree on in advance. As it sounds like you two never discussed it, if you decide to bring legal action, the courts will decide what’s reasonable in the circumstances.
Here are two recent decisions from the tribunal that handles disputes under $5,000. In this decision, the roommate received one day’s notice to vacate; that was found to be unreasonable. In this one, the roommate was given seven days notice to vacate, also judged unreasonable. You can find other decisions by this online tribunal — called the Civil Resolution Tribunal — on this website. One of the themes in the tribunal decisions is the importance of treating each other respectfully. Putting things in writing at each stage is one way to do that — and it helps prove your position if you decide to sue.
Because these kinds of disputes between roommates fall outside the Residential Tenancy Act, bringing legal action for damages is, unfortunately, often the only way to resolve them. The good news is that this recently created Civil Resolution Tribunal is much faster and less expensive than going to Small Claims Court — which until a couple of years ago was the only legal avenue available.