How do I handle a stalker?

not really a 'stalker' in a criminal sense, but weird nonetheless. I work at a video store and talk about movies to the customers, well this one customer started coming in more often and of course i was friendly in a professional way. what i didn't realize is that he apparently is madly in love with me. he came in the store 2 days ago and gave me a note professing his love and sadly expressing his loneliness and desperation and how he feels he is repulsive to women. this note is seriously borderline suicidal. for one, he should have just asked me out so i could've told him about my boyfriend, and we could've skipped this whole awkward situation. i don't know what to do about this, should i just tell him about my boyfriend and hope he doesn't follow me home or commit suicide or should i take this to the authorities?