I'm literally breaking down

So my best friend is having her birthday party soon and my ex (we broke up about a long ago) will be there. How do I handle tho because I just about cry ect time I see his face on snapchat and have no idea how I'll handle seeing him in person. I was planning on drinking even before I knew he was here btw. He's only coming because his friends are coming and shit which is fair enough. How I deal with it on the night? Do I stat (make out) with someone to get back at him? Do I get completely paralytic drunk to forget he's there. Plz help. He'll go and is going and I want to go to