Isn't the exit something every entrepreneur has thought of? At least once? The years of hard work, struggle, and courage would finally pay off with an "exit." I can assure you that your investor has already thought about an exit even before having invested in your company. Most probably, he has thought about the exit a lot. At some point in your relationship, your investor is likely to sell his shares to earn as much profit as possible. It is his nature; that's the business model of an investor.
You can give a peek on how this day could look like by adding an exit (strategy) slide to your pitch deck. On this slide, you should list companies that may be interested in buying your company someday. You can also add a list of companies that are similar to yours that have successfully sold their companies. Don't forget to name the buyer and the valuation at the time of the exit.
Be careful when presenting your exit strategy slide. One thing investors don't like to see are entrepreneurs who are just doing business for the exit. Furthermore, it could be seen as unfavorable if you look for potential buyers instead of thinking about how to become the market leader in your area.