Want to know how do I go about asking a Guy At work out, So confused !!!?

Right so I want to tell him how much I think about him all the time To cut long story short we went out twice , had a good time n then he turns around and says he cant have a 'relationship' with me as we work together, but there was no mention of he is not interested in me and all that crap!! , i mean the way he did it was he asked me out again to have a drink and have a chat , we had a good time and at the end of the night he said it he cant do it!! I mean i neva asked for anything like a date again or to have a relationship initially, but he came up with the having a secret relaltionship out of work and then backed off, I don't no what to think of him ,, He does talk to me at work and checks me out when I m not looking, sits near my desk,,!! I want to tell him how I feel I don't want any think in return, but want to get it off my chest, Don't no how to do it,, Some help needed.. Please give some suggestions,He is definitely single and available. well lately i have been ignoring him at work as I was angry at him for turning me down !! But now I like him and want to get to know him better!!! x