I guess "the only healthy option" isn't right, but she is currently one of the healthiest relationships. It also depends on what you consider healthy or not. Sage's path isn't so bad because they both know its cheating but it's 'justifiable'. Quinn plays games with MC but she doesn't pretend she's anything she isn't. Jill has baggage hidden somewhere but maybe it's no biggie.
I'm sure by the end (unless DPC makes them fight in a battle royale to kill off half the LIs or something) they'll all be in a healthier spot but currently they're all pretty bad.
To add on to Shazba's answer because he hit a lot of the key points:
- Cathy, Jade, and Bella all have an awkward power dynamic problem as faculty. MC isn't in a class of Bella's yet so its not quite a big deal.
- Sage, Bella, Josy and Maya's relationship with MC all start with cheating.
- Maya's especially started out with a bunch of lies. That's behind them, though, so maybe null point.
- Quinn's got so much baggage and she's such bad news
- Jill's so far the second best, but she has the sword of plotocles above her head with Bella and that pamphlet. Plus the MC asks her out to piss Tybalt off first, his feelings coming second.
- Almost all of the LIs have played head games with the MC at some point.
- Camila isn't a main LI and that is unhealthy for us, the players.
Nicole was upfront, she expressed hesitation but MC was mature enough to convince her otherwise. He knows she has a kid and that she's a stripper. All her baggage is on the table and they interact a fairly normal way for an early couple without any dicking around, cheating, lying, so on. Sure, it's mostly sex but that's not unusual.
The biggest problem is the age gap, but again MC is written to be pretty damn mature for his age so that would mostly make an awkward relationship with her kid. And he would probably have to tell her not to blow any clients anymore if they get exclusive.