Three things. No order.

Thought. Which is almost contradictory since thought and imagination isn't exactly in our reality. In my brain, anything is possible. I can be and do whatever I please. Thinking of concepts, thinking of stories, thinking of anything, just makes me happy. I love to think. Few (well, two total) things in reality make me happy in any regard. Everything feels too bleak to get much joy out of.

My girlfriend also fills me up with joy, when I'm alone with her, she makes me feel like I can do anything and everything I want to like in my thoughts, she's helped me through so many things, whenever I'm stressed I can always go to her, and she makes me feel happier, being with her is always the highlight of my day. Sadly, I don't get much privacy, so I don't get to be as alone with her as I would like, or I guess could even be considered adequate.

My friends. They've also given me emotional support and made me happy. I am lucky to have them, I do hate being alone.