This isn't really accurate. The event chains aren't triggered by having affection, they're triggered by completing events. Beach 1, which was the first event chain with missable lust events, required the completion of a vast swathe of character events. Similarly Halloween, Christmas, Dorm Wars, and the 2nd iteration of those. If you're playing the game patch-to-patch, you will never boot up the game and get launched into a main event chain unless you've finished all the content in the past, in which case your problem still isn't affection, it's just which events you've completed.
Here's a cheat sheet of lust-based content per event chain, with what lust level you need to not miss anything:
Beach 1: Lust 10, Ami/Ayane/Futaba (Futaba's isn't a full event, just additional dialogue in an event)
Halloween 1: Lust 10, Sara/Haruka
Christmas 1: Lust 10, Chika/Futaba
Dorm Wars: Lust 15, Ayane+Kirin/Futaba
3rd Reset: Lust 15, Ami
Beach 2: Lust 20, Kirin/Chika/Makoto
Halloween 2: Lust 20, Ami
Christmas 2: Lust 20, Ayane/Sara+Haruka/Kirin