Drama! Was this an appropriate way to deal with being hit on whilst in a relationship?

A man has been constantly flirting with me even though I say that I am seeing someone, not interested, etc. Finally, I snapped and said: okay, If you're unable to be purely friends with me then don't chat with me anymore. It's not fair! Of course I'll start taking it seriously after a while I have pretty strong feelings for this guy, just so you know What are the pros and cons of saying this, and do you think that it sounds strong enough to get him to leave me alone in that way? I love my partner, and want no one else to destroy our relationship