I can only imagine how stressful it must be. I knew a guy who was being stalked, mostly online, by a woman he went on one date with (and, according to him, never slept with) but she decided he was the one for her and didn't take rejection well. Stalkers are obsessive people who rarely can be reasoned with - even the slightest contact with them flames the obsession.
You may have done some research already but maybe see if any of these links are of help
https😕/www.google.com.au/#q=dealing+with+stalkers