It occurs to me that it might be helpful to have a game plan for the graduation. Having a game plan always helped me because I don't think on my feet very well. I need something to focus on and I tried not to be blindsided.
So for instance you know you'll see him so do not engage. Nod and move on to another spot. Ignore their words, glances, etc. I needed a plan of what I would say in my head or where I would walk to sometimes get through things like this. When things begin to wind down leave to eliminate the opportunity for more awkwardness. Have a plan on how to avoid a conflict. Do you have a friend that can go with you? One that you can confide in so she knows the deal and you can have a signal that means "I need out of this situation for a minute" or something like that. I did not have that friend but I sure longed for one! Or one that can come and touch your elbow if she notices you are beginning to engage.