They had both agreed to attend the wedding because they are dear friends with the bride and groom, but they are not back together. It was an emotional wedding, and they held hands but only because they will always care about each other.
They are exes that everyone can aspire to be like because they are mature and kind and gracious to each other. They were happy to see each other and spend time together at the wedding, but they are not a couple. They're both going to go out with other people, and they want each other to be happy.