I need coping mechanisms - thank you

[daisy pooh]

My ex and I dated for about three months about a year ago and it ended really badly. He had lots of issues and was not a good boyfriend, but I was too weak to call it off, ended up writing him a bunch of nasty (but honest) things, he called it off, I stupidly begged him to stay with me, he called me two-faced, pathetic and then he even insulted me on his social networks (a few times, the last time being several months after he had called it off). And this ex is now going to be the best man at the wedding where I am the maid of honour. I am a pretty anxious person and I am not sure how I will handle seeing him. I had a feeling he wanted to destroy me post-break up, there was so much vindictive and unnecessarily nasty behaviour on his part. I am pretty sure he'll behave at the wedding, and so will I, but my body already is going into a state of anxiety just thinking about it. I am afraid I'll start crying or faint or throw up. I am by no means a skittish person, but this man played with my head so much and I felt bullied by him and manipulated to the extent I have no idea what to do. He's a charmer and everybody thinks he's the kindest person in the world. I don't. I just need some coping mechanisms to get through the day. Any advice will help. Thank you.