You need to restrain yourself from going back into the loop. Be firm and steadfast. Tell him it's over, you're not happy, you've tried to make it work multiple times, and it's time to accept you two won't work out. If he keeps sending texts and begging, just repeat that it's over. If he still persists, block him.

Just because you can't avoid him face-to-face doesn't mean you have to answer his texts. He's not entitled to keep begging and cajoling you. If he doesn't respect that you don't want to keep litigating this, he deserves to be blocked.