The games Loyalty/Corruption system kinda sucks. It would make more sense if this wasn't a sandbox and more of a linear "choices matter" kind of story. It seems you can't reliably increase either your Loyalty or Corruption, and since you need a certain amount of either to progress your relationship with any of the girls, it becomes a confusing mess trying to figure out what interactions you still have available to increase one or the other.

This is incorrect. Currently, you can increase your corruption reliably through club events in game. (You cannot increase your loyalty though you will be able to in future updates through church)

But I understand your problem, since in some cases it doesn't tell you what does what. That still needs improvement through tutorial and a walkthrough.