Help please?

There is a guy that is the best looking person I have ever seen up close. I want to approach him. The only problem is sometimes he seems interested and others he does not. We have been e-mailing back and forth some. He sent me a message at the beginning of the week just to say hi and for me to have a great week. But then when he sees me at the gym in person he won't say anything. What do I do? He always looks at me and makes eye contact in a room full of people. When I catch him looking at me, he just looks away. We are adults so this feels like a kiddie game to me.