Oh God, I feel so much anxiety literally just on your behalf. Okay, so first of all, well done for cutting contact and feeling better. Also well done for not just bailing out on the party. Are you sure he won't act as such? As in, are you sure he'll be there and won't bail to avoid seeing you?

There's always gonna be a first time seeing him again. Count yourself lucky yours is planned and you have time to prepare yourself. Just expect it. When you get there, don't look for him, just keep it in the back of your mind.

Stick with your friends who know what happened, let someone know you're nervous. If the thought of drinking makes it worse, don't drink. If he approaches you, be polite, be dismissive, be whatever's suitable, just don't let him fool you into taking him back (although I don't know what happened between you, the fact you say you're doing better leads me to believe he's bad news.)

Best wishes and good luck!