So I like this guy. I've never really talked to him but he seems great. Whenever I see him we make eye contact and I've even got a flirty smile from him recently. Somedays I think he notices me and then other days I don't think he does. I'm afraid to talk to him for the last three months unless I needed his help with something and then we often make eye contact and he acts as if he's waiting for me to say something? How can I tell if he's interested?

I think you should definitely talk to him if he's been giving you the flirty eye that he's probably dying for you to talk to him

Well when we talk it's just like he doesn't want to finish the conversation or he's too shy too. He mentioned to me like three weeks ago when he asked where I was from that he had a girlfriend who lived up that way and ever since then we haven't had a real conversation. I get a hi from him once in a while. I think he might know how I feel. But then when he told me he had a girlfriend I know that he doesn't like me so I just set my feelings aside for him and I just gave it up. But lately I've been getting a hey from him whenever he sees me and it's kind of nice and the other day he noticed me smiling after he said hi to me I was in a good mood all day and I seemed really distraught before that everyone told me

There isn't much you can do as long as he's still in a relationship. Check out these guidelines for insight:

https://www.askmehelpdesk.com/dating/guidlines-what-do-do-if-person-like-already-relationship-463250.html