Ok, before we can start any kind of discussion over whether love/hate changes need to be rebalanced, we need to know exactly what causes changes in love or hate. So I've gone through the code, to get a full list.
Love+:
Free a slave (10)
Increase accomodations (slave) (No gain at level 0 accomodation, else double freegirl gain)
Increase accomodations (free) (1 point per turn for lvl 1 accomodation and 1 point for every 3 levels above, IF happiness = 100 AND (accomodation level is higher than the girl's level if girl's level is less than 6))
Happiness is 100 (2)
House slider <= 30 (varies)
Love-:
House slider > 60 (varies, free girls only)
Enslave (-10)
Rape interactions (-2)
Scold interactions (varies depending on spirit, -1 to -4)
Torture a girl (varies, -2 or -5)
Slave in the dungeon for a turn (-1 if feeding, -2 if starving)
Free girl in the dungeon for a turn (-4 if feeding, -5 if starving)
Her love of the PC made the difference in her decision to obey (-1)
Take away her money (slave -5, free -30)
Hurt (-1)
Badly hurt (-1 additional)
Tired (-1)
Extremely tired (-1 additional)
Health deteriorated from being tired (-1)
Unhappy free girl (-2)
Security girl was defeated (-20)
Girl was raped by customers (-20)
Hate+
House slider > 60 (varies, free girls only)
Enslave (5)
Rape interactions (3)
Take away her money (slave 5, free 30)
Any girl dies (1)
Low happiness (varies depending on how low it is)
Girl in dungeon (1 / starving free girl 4)
Hurt (1)
Badly hurt (1 additional)
Very tired (1)
Tortured (1 or 3)
Security girl was defeated (20)
Girl was kidnapped (50)
Girl was raped by customers (20)
Decrease accomodations to equal or less than girl's level, IF girl's level is less than 6 AND happiness = 0 (varies)
Hate-
House slider <= 30
Increase accomodations (slave) (No loss at level 0 accomodation, else double freegirl loss)
Increase accomodations (free) (-1 point per turn for lvl 1 accomodation and -1 point for every 3 levels above, IF happiness = 100 AND (accomodation level is higher than the girl's level if girl's level is less than 6))
Ok, I think I got all of it in there. I may have missed one or two special cases.
From what I can tell here, as long as you're treating the girl right and her happiness is 100, her love will rise quickly, especially if you have her at an accomodation level higher than her level. (doesn't necessarily have any effect on her hate). Given that all girls need 255 experience to increase in level, and all jobs give around 5 experience (ignoring quick/slow learner), it takes 51 turns to level. A level 0 girl will, if treated well (happiness stays at 100) max out her love in 50 turns. If also a free girl's accomodation level is 2, she will max out in 33 turns, and a slave girl also at accomodation level 1 will max out in 25 turns. In all cases, you will max her love before she even gains her first level.
So, this needs to be changed, and I'll be looking at this as my next project after I have the jobs code finished.