I agree with Samuel and Samuel.

Taking it a step farther, under Washington law, nonuse will not normally terminate an easement. That raises the question of what will terminate an easement. Your neighbor is right about the adverse possession time period of ten years, but wrong about what has to happen for those ten years.

To extinguish the easement, the owner of the burdened property (your neighbor) must effectively prevent you from using the easement for ten years. A fence with a locked gate which you have no key would be an example. Other physical obstructions would work too. Generally the whole easement has to be obstructed, and partial obstructions that do not interfere with normal use don't count.

The other possible basis would be if the owner of your property obtained and established some alternative access and abandoned the easement. This would be very hard to prove, but you should consider it.

Most judges will start with a strong presumption that the easement is still in place. This would still be true if 50 years had passed instead of 18.