This guide will allow you, as non-patreon supporter, to read some interesting stuff about the game, that was posted by the creator almost a year ago, during development of the game. I can therefor not tell you if this is exactly how it works in current game, or if/how it changed. Use the info, but more importantly, play the game and do not try to be perfect...
Romance - Breakup - Trust Level
One of the features implemented in General Practitioner in the latest updates (and in future ones as well) is the so-called "jealousy" feature.
Remember it is a small town, and even if you were discreet, everybody knows.
Starting from Claudia in 0.0.24 and continuing with Erika in 0.0.25 it comes a point where your past actions will need to be faced in front of your romance partner. While General Practitioner is not a stats-based game, meaning you don't have to grind stats in order to progress the story, stats will play a role in determining if a relationship will continue or not.
Hating and Loving
Of course every character is different, so what bothers someone might not bother someone else. This is especially true in GP, because people will tend to trust each other and maybe distrust someone "just because".
Let's take Erika for example: she doesn't notice (or care) if you have a relationship with Claudia, Elisa or Christina, but she WILL confront you if you happen to have a relationship (even a past one) with Rita or Kiko (because she can't stand medical professionals having a flirt with patients) and she will also be disappointed if you had sex (or you were in a relationship) with her close friends Vanessa or Aaron.
Also, she can't stand bisexuality in her partners (you might agree or not, but that's her opinion and not every character has the same one) and she will be more ♥♥♥ off if you had a relationship with Aaron more than if you did with Vanessa.
Of course past relationship "stack" together, so the bad effect on her will increase proportionally as the partners you had.
That means that every relationship with the above people will have you decrease her trust by a certain number of points (usually 10). You will also be asked some conversation choices that can increase or further decrease this value at some point.
That's where past deeds with your partner come into action. If you behaved in a certain way (in Erika's case for example: have you blackmailed her into sex at the gym?) during the course of the game she will remember those actions and decrease her trust even further.
If you behaved well and have a strong relationship you won't reach her "tolerance limit" and she will trust you enough to keep your relationship safe and sound.
Each character has a "trust tolerance level" below of which they will break up with you no matter what. Then again, since every character is different one might have a very high tolerance while other won't.
For example Claudia's trust level to stay with you must be higher than 60, while Erika's must be higher than 40 and Aaron must be higher than 70.
This has been done to "simulate" real relationships, because different people tend to be harder or easier to be with and your own deeds might mean more or less to them.
Still, the relationship system has been built not to be too much hard on players. The game won't feature a gameover and the story will unwrap with different endings for each romance.
Note: I recommend you NOT to look for a "perfect ending" but to enjoy the game trying to take into the shoes of Dr. Jones, making choices as you would in his situation.