Quitting on client due to school

I’ve been walking a pup everyday twice a day for the last month now. Unfortunately, I am going back to school full time in September and I know I won’t be able to attend to him as often… I can’t seem to bring myself to telling the owner as I am really fond of her and her dog and I want to keep the relationship.

Tonight when I go walk him, I’m going to tell the owner in person. How should I go about this? How can I word in it a way that expresses my interest in walking him on the occasion (ie. holidays/ if she’s unable to find someone else, etc.)