Well, i havnt the slightest idea about modules, apart from the few ive tested, but the default game has two forms of stalking built into it already:
1. The stupid one, where the NPC will cling onto you and follow you around (which is mighty annoying, by the way...)
2. A more refined stalking mechanic, where the NPC will follow you around at a distance, not interact with you, but hang around in the same area as you, while looking in your direction:
Imagine youre in the locker room of the school, standing next to the lockers themselves. An NPC with high love count will enter the room, but rather than clinging onto you like example 1, it will just walk around, stopping from time to time to look at you, then move about some more, repeat. If you move from the locker room to, say, the courtyard - the NPC might follow you there, and if youre standing next to the tables - the NPC will chill on the far side of the area, while facing you.
With that said, i have no idea how the stalker module actually works (since i find it pointless, given what ive just described). What is even the intent of the module, if stalking is already in the game? Some things will just never be known...