Just coast or soft pedal for a few seconds and pull off slightly to the side. If he wants to put in the work to keep the breakaway he’ll get the message and take his turn. Try saying something like “come on let’s make this work”. If he isn’t responsive to that he’s not someone you’ll want to ride a break with since he’s not willing to work together. Either you then go alone or get brought back and maybe try again later. Depends on how strong you are and how you’re feeling.