What brings you joy? Here are a few things from my list (in no particular order):
Simply being with people I love, doing something together
Coming up with ideas and making things up
Finding things out, solving interesting problems
Learning new skills
Walking, running, cycling or swimming, surrounded by nature
Listening to music and playing music
Wandering through busy cities
At first sight, the list looks quite random.
If you dig deeper though, there is a pattern: all these activities are about immersing myself in something, resonating to something, being at one with something. They all involve some interaction. Many involve solitude, but this solitude is of a very special kind: the solitude of losing myself, the solitude of total immersion.
So I believe true happiness is about being at one with something. When you are an integral part of something - there is a reason for you to exist. A purpose, if you will, even though the word purpose is too loaded. The whole, of which you are a part, needs you to be a part. This whole can be anything you want, large or small, as long as it's bigger than yourself. It can be your family, your work of art, your project, or even Universe at large.
The larger the whole is - the harder it is to truly belong, to see and feel yourself as an integral part of it. Very few enlightened people can truly and continuously feel that they are at one with Universe as a whole. The rest of us have to find smaller things to belong to.
So don't be afraid to find something (or somebody) to attach to, to be at one with. It doesn't have to be something or somebody special. Because once you are at one, you two will be special by the very fact of your oneness.
Don't be afraid to need somebody, or to have somebody who needs you. Any oneness is temporary, except for oneness with the whole world. But why knowing that should stop you from enjoying oneness while it lasts?