I'd say date two over dessert. "Hey, as a heads up I have a stalker. Haven't seen her in a little while, but [insert brief recap here]". Before sex is on the table for sure. Maybe it's because I'm in the middle of a Criminal Minds re-watch, but intimacy with someone else can be a trigger for escalating behavior from a stalker and that's the kind of information I'd want before hand as a potential partner of the stalked person.