Yet she makes snide comments about MC's best friend Derek.
His point is that MC's 'true self' doesn't differ that much between LI, unless he is with Jill. Check his bios entries, he doesn't have sex with her,
he makes love. Jill is the only LI he protects from the walk of shame and in the most corny way by giving the diks a speech about 'his girlfriend' etc. And just like
noctarima said, its not that Jill is twirling her landing strip mustache manipulating the MC, its just her demeanor and MC's inherently trying to please her that make the MC act so different. You might not mind it, but you can't argue its not noticeable.