Wow Juicy workplace Lust affairs, and you only just started... go you good thing.. Unfortunatly the fact a guy blushes under the gaze of a woman, doesnt necessarily guarantee he has interests in you, and after being paid a compliment by another woman will surely bring upon a smile.
You said he ackowledged you by saying "hey" in passing this seems to justify him as a nice guy and admitting openly to having a girlfriend substantiates him as a genuine fellow, so if you can single out men of his calibre so quickly I cant help but think you will be with faithfull fella in no time.
