Mixed feelings about Father's day

Going to see my kids and grandkids this afternoon for Father's day. My ex has a pool at the house and the kids wanted a pool party so will be going there this afternoon. Only time I see my ex is on holidays, b-days or special occasions like this. As much as I want to seem the kids and grandkids I wish I could just bow out of the day. As time goes on I more and more hate being around my ex.