Sit him down and say "sorry, but it's not working out. No hard feelings, I wish you the best of luck, but this isn't the right project for you."
You did the right thing by vesting options, and it seems clear that there is no fit for him. So, the outcome is inevitable, you owe him nothing but politeness, the rest is just timing.
You did the right thing by vesting options, and it seems clear that there is no fit for him. So, the outcome is inevitable, you owe him nothing but politeness, the rest is just timing.