Pretty sure that FL is manipulative and the stalker was her former victim ("I did everything for you"). Also at the grill stuff when FL was bombarded with notifs, she prob called the stalker to come then stalker saw FL on the ground, helpless. It also doesn't make sense how he's there when FL gave ML cabbage cakes. Set-up? Idk. FL most likely got bored with stalker and went on to find another or smth.
Kimi ni Koisuru Satsujinki