Well. living with an 18 year old son at home hardly constitutes "living alone". And I think it's a big jump to stalking.
Nonetheless, it's important to be completely clear with people like this. Something along the lines of:
"I'm sorry if I've given you the wrong impression, but I'm not interested in you and I think it is highly inappropriate for you, as a married man, to be contacting me like this. Please stop."
