I'm the register agent for two different business. If being sued, can they come after both business, i'm only the agent?

Not likely, unless there is some relationship between the general contracting entity and the retail entity, and the plaintiff has a legitimate cause of action against both business entities. When you serve as the registered agent for a corporation, limited liability company, partnership or other business entity, you do so in a representative capacity, and you incur no personal liability for the actions of the business merely by serving as its registered agent.

By serving as registered agent, you have agreed to accept "service of process"----that is you have agreed to represent the business when it is being sued, and to accept, on its behalf, copies of the pleadings and other court filings in any lawsuit or other proceeding against the business. You do not have to be an officer, director, shareholder, manager, member or partner of the represented company. In fact, many attorneys and law firms serve as the registered agent of their clients, and there are corporate agent services (e.g., CT Corp., CSC, NRAI) available in every state capital to serve as your business' registered agent for an annual fee (typically, $150 to $275).

If your business is organized as a corporation, limited liability company, limited partnership or other form of registered business entity, you must have a registered agent in the state where the business was incorporated or organized, and also in every other state where you are doing business. What constitutes "doing business" varies from state to state, and you should consult with a business or corporate attorney licensed in the particular state if you have any questions.