How can you tell if a guy is still interested in you?

Additional Info: I met this guy at work and he was flirting with me constantly. He would stare at me alot and he would compliment me. After a couple of months i built up enough courage to ask him how he felt and he had revealed to me that if he was not in a relationship he would have to say that he did like me. I then revealed that i liked him also. Ever since then it has been kinda weird at work but he still gazes at me and now we both go back in forth with staring and avoiding each other. My question is i am unsure if he is still even interested in me because he avoids me sometimes. I understand he has a girlfriend which is why i avoid him ( i dont want to get involved with his situation) but sometimes he still tries to get my attention and sucks me back in.... please help???