This is a valid complaint that I keep forgetting to address. I have an idea to make it easier to understand, but that won't help you now.
With the current version, you know if Amelia is seduced if, while Lamia is awake, she periodically has the image of her giving heart-hands with a pink magic circle. If Amelia is seduced, the Lamia has to re-cast the spell to keep it going. If Amelia is not seduced, this will be a stomach-shake disruption instead.
Lamia will do it 2-4 times per day. Amelia needs to have her stats in a certain range, and she will be able to resist it. Resist it 2-4 times, and the spell will wear off. If you 'participate', the spell will be reapplied. There's more information in Help > Predator Tips - Spoilers if you want to read Lamia's tip page.