その交わった視線で 私なんてすぐ乱されるから
I understand the sentence is "As our lines intersects, I am throw into into disarray" aka the narrator says because she loves him, when their eyes meet, she panics.
What confused me is, why is the passive used here over the causative passive? Given she's being made 乱す by his gaze?
乱す is already a transitive verb meaning "to disturb (someone psychologically)" or "to stir up", so its passive form ("to be disturbed") is sufficient, and you don't have to make it causative.
The intransitive counterpart of 乱す is 乱れる. It's possible to use its causative-passive form and say 私なんてすぐ乱れさせられるから instead, but this sounds less natural because it's unnecessarily wordy.
