Also, he can make sure that engagement doesn't happen or at least make it that the girl doesn't get too obsessed with the thought of becoming his wife and maybe just an ally instead. Plus now he potentially has the upper hand on the prince so he can plan countermeasures or even some sort of preemptive strike. There's so many other things he could do, too. Gotta use that time travel cheat to it's fullest!
Not sure how they're planning to progress with the story now and what he might do the same or different (is he still gonna do all that fighting? And now we know that he based his shops off of a forgotten memory of Erin/her eyes, so is he gonna still open them but this time while knowing it's for her?) but I'm looking forward to their reunion! Though this time she might be the freaked out one at his potential enthusiasm/impatience without that initial effect of them spell lol hopefully she at least remembers that they met as kids, but considering how young she is and her ditzyness, I doubt she will...