Celebrating the happiness of others requires a generosity of spirit that we often find only in the process.
The struggle with being happy for others presents itself early in life. If a child wants a toy and another child has it, the child will try to get it or will break down in tears. Those primal feelings are still present in most of us, and we have to acknowledge them when they arise. At the same time, it is when we care enough for someone to let go of what we want for ourselves that we grow as people. It can be a difficult dance to find ourselves suspended between wanting the toy and throwing a party for our friend who got the toy. Yet, it is in throwing the party that we share in the joy--and, to some extent, the toy--rather than cutting ourselves out of it.
Extending ourselves to celebrate the happiness of others requires a generosity of spirit that we sometimes find only in the process of doing it. So when your best friend moves to Spain with the person you had a crush on, tend to your broken heart but throw them a going away party too.