One tenant attempting to break lease due to roommate dispute

[Michael Gordon]

So, I recently had my first tenants move in February 1st in Washington State. There are 2 tenants, they've been here about 3 weeks and today I learned that they're not getting along and I believe that one of them intends to move out and break the lease. I dont have any issues with the person who intends to stay but he obviously wouldn't be able to pay rent on his own. I'm definitely not opposed to them finding a new roommate so long as they meet all the requirements and I'll re do the lease at that point. My question is what do I do in the meantime? I believe the original lessee will be required to pay his fair share up until the point that a new roommate takes over I'm just not sure how to go about ensuring this gets enforced. The lease is not separated per tenant, its just one monthly rent, both current tenants have signed.