Everyone likes positive attention. This man was enjoying the attention and probably figured you already were involved with someone. You did change things when you shared that you have a crush on him. That's like saying you are interested in more than just flirting. Well, you learned that next time you have an attraction like this it's best to find out if the man is married/committed first. And some men do like to enjoy the company of an attractive female coworker but only want to keep it as a positive coworker/collegue experience and nothing more.

I think it may be helpful for you to put the shoe on the other foot where if you were married and committed and an attractive man entered the place of your employment and you began to enjoy his attention, even went for coffee etc. and he changed that by admitting he had a crush on you. You may have felt safe to flirt in a very platonic way and did not expect this guy to think MORE could happen. People DO invest a lot in their marriage, it's not a simple "If I meet some attractive woman it's easy to end things". Walking away from a marriage can mean giving up a great deal for a person. And you don't really want a man that finds it easy to cheat either.

You also need to be mindful when it comes to your work environment, you don't want to develop into "that woman who flirts and cheats and chases men at work". There are women who consider work environments "hunting grounds" and they are not looked upon favorably. The other challenge is that men DO have to be careful now in the workforce and make sure they don't do anything that crosses the lines where a woman can suddenly cry "he is treating me inappropriately".