Not sure about the low relationship thing.
I think Ian only finds out, from Jeremy at least, if Lena does anything sexual during the bar gig. If you sleep with others outside that specific portion of the story I don't think Ian becomes aware yet.
That's correct.
The relationship level with Jeremy doesn't matter at all btw, he'll always tell Ian what he knows. But Lena can e.g. "get over" Axel and then fuck him only when she's about to depart for the beach house, and Ian won't be aware she's hooked up with him, because Jeremy obviously couldn't have known that when he was meeting with Ian earlier.
The
lena_cheating
flag which triggers Jeremy's report is set if Lena fucks Mike, Mark, Marcel, Jack, Jeremy, in Ch. 10 or 11, or Axel before the talk with Jeremy takes place. Ironically, it seems that fucking Robert goes undetected :hidethepain: