I believe the joy of the apostles was overwhelming when they saw the risen Lord. The first unbelief was gone and true joy filled their hearts. But there is something unknown in this joy. Jesus Christ told them that he would have to leave and go back to His Father. The Advocate would come but they would have to wait for him.
We live in a world where people gain and lose friends so fast. They call anybody they know a friend, but after a few moths or years they are changing them for other friends. So at the end they do not have real friends, but they know a lot of people.
Aristotle said that friends are one soul split between two bodies. For ancient Greeks friendship was more valuable than marriage. It was the highest level of a relationship. Jesus Christ called his disciples friends because he had revealed to them the truth about His Father. I think the time between the Resurrection and the Assention was the most important time of their friendship. For these 40 days all his disciples learned to be fully immersed in this friendship. They trusted Jesus Christ to the end. They lost him once, but now he was with them again. Every moment was so precious and important. They didn't understand what was going on but they were with their Friend. For 40 days Christ was preparing them to say "goodbye, I will see you next time in heaven."
This is the friendship we are looking for. Whoever has a true friend is the richest person in the world. We have a friend that won over death. He is always looking for us and comes with His grace. There is one thing we have to learn - to say goodbye to this world and go to the Father. Each one of us will have to do it in our own time.