What is it like running into your ex??

I was in a relationship with this guy and decided to elope one day.
I was all ready with all essentials packed in my bag waiting at the Airport only to realize he never showed up. A few hours later he broke up with me over a text saying he couldn't do it. I went back home and became miserable in my life watching my parents unconditionally loving me, clueless of what I was gonna do.

4 years now, my husband (they both work in the same company) has asked me to join him in his office party!

What do I do if I run into him? Or make eye contact??