Has anybody here ever dealt with stalkers? I don't know what to do. I…

Has anybody here ever dealt with stalkers? I don't know what to do. I saw my ex roommates as customers at my work yesterday, but when our relationship turned sour we were over 2100 miles away on the other side of the country. This world is too big for us to just randomly be in the same place at the same time... right? Am I overreacting? Should I just write it off as a coincidence?