He responded poorly (understatement) to the rejection of someone who he knew was in a relationship at the time. This is why I have a rule of never dating anyone who works where I work, not even in other departments. It just creates too much trouble. Once it's known that you date people in the office, others who are interested in you (but you may not be interested in them) may pursue you. Once you start rejecting them you can't give a blanket response of: I don't date people from work. Feelings get hurt, and people do stupid things once that happens.