How do you put yourself out there? How much work needs to be put in when you want to be with someone?

I don't really understand dating or relationships. I had a messed up childhood, and I never been in a relationship because of it. I'm 29, and I've met someone I like. I thought he liked me, but he's gone away to get help for himself. While he's been gone, I realize how much he meant to me. I never put myself out there. I never told him I liked him. I was too shy to show him. He showed me signs of interest, well I thought they were signs. He would go out of his way to talk to me, he would cheer me up when I was having a bad day. I catch him looking at me. I don't know how to take that. I don't know how to react. One of the last times I saw him, he said to me "Sometimes I don't think you like me." I just said, I like everyone I work with. I didn't realize I came off like that. I don't know what to do....should I move on? Should I try to message him on facebook, and tell him I miss him?