How do I cope with being on call for clients who treat me as a service?

You can hold the biggest client relationships, and you are worn out from being on call for people who see you as a service, not a person. That is a specific kind of tired, always available, rarely appreciated, valued for your responsiveness more than your humanity. The exhaustion is real and it is fair. Part of the load, though, comes from believing you must be endlessly available to be worth keeping. You do not. The clients worth having respect a professional with boundaries more than a servant with none. Being reachable is part of the job; being owned around the clock is not. Some of the on-call feeling is a rule you can loosen, not a law. Start small and set one boundary you can hold, a window at night that is yours, a response time that is prompt but human, not instant. Protect it quietly and consistently. You are a person who provides a service, not a service that happens to be a person. Let your own life have a claim on you too.