The responsibility of maintain an easement varies from state to state. Generally speaking, the easement holder, i.e., your neighbor, has the responsibility of maintaining it, if the easement document does not specify such. Your first and foremost task is to go back to the easement document to find out if the document says anything about the responsibility of maintaining it. If not, then find a local attorney to search pertaining state law. I would think that under MA state law your neighibor should share the maintenance and by shoveling snow onto your driveway, or the easement, he effectively breached the easement agreement. This may provide you a chance to terminate the easement for unauthorized use and overburdening the easement.