How Love Paths work:
There are 3 love paths - one for each LI - Glade, Kasula and Lorelei.
At the start, each Love Path is linear. You get a choice, and if you choose the correct option, the game will act as if you're on that Li's path, but if you choose wrong, then you lose their path and the game will act as if the MC is uninterested in that LI. All these choices are fairly straight-forward (such as choosing to spend time with that LI rather than brushing them off), and they're all considered to be important choices.
You must be on at least one LI Love Path. Thus, if you've lost Kasula's path and Lorelei's path, then the game will automatically put you on Glade's Love path when the choice comes around. This also means if you're only on one Love Path, the game will skip the choices to drop that love path. This ensures there are no monk runs.
Halfway through Chapter Two, the game will then ask you which LI you would like to take to the Ball. Now, you can kick the can down the road, but ultimately, you will have to choose. At this point, the LIs will have decided if they're interested in the MC or not and will act accordingly. So even if you choose to take Kasula to the Ball, Lorelei will still act interested in the MC if you were on her Love Path before choosing Kasula.
The easiest way to describe the system is using 'tiers'. To put it simply, the game will classify each LI into a tier based on the choices the player has made. The four tiers are - Primary LI, Secondary LI, Tertiary LI and Lost Path LI.
The game will always act as if the MC is interested in the Primary LI and you won't be given choices whether or not to pursue that LI. This means that the game will automatically make the MC spend time with the primary LI, as well as kiss/cuddle the primary LI.
The game will also act as if the MC is interested in Secondary LIs. This means the MC will automatically spend time with secondary LIs, but the player will be asked whenever they want to kiss/cuddle the Secondary LIs.
On the other hand, the game will always ask the MC whether he wants to spend time with Tertiary LIs, as well as kiss or cuddle with them. As for the Lost Path LI, the game will skip all non-plot content with that LI with the exception of a few small encounters in some cases.
There must always be one, and only one, primary LI. The other tiers have no restrictions meaning you can have 2 Secondary LIs if you wanted (at least until towards the end).
How does this tie into everything? When you invite a LI to the Ball, they become the Primary LI. Whichever other LIs you're on the Love Path for become Tertiary LIs while the others become part of the Lost Path LI tier.
Once you lose a LI's path, you can no longer get back on their path with a couple of exceptions. For example, if you're on the King Lovell Allegiance Path and not on the Lorelei Path, you get a second chance to get back on Lorelei's path. If you choose not to spend time with a Tertiary LI, you lose their path.
For a LI to go from a Tertiary LI to a Secondary LI, it's rather simple. Once you kiss a Tertiary LI, they become a Secondary LI as the game will treat that as a sign you're romantically interested in that LI. If you continually choose not to kiss/cuddle a Secondary LI, then they will become a Tertiary LI after a while.
For a LI to go from a Secondary LI to a Primary LI, it's a little more complicated. You must continuously kiss/cuddle the Secondary LI, which won't go down well with the Primary LI. Eventually, you will be given an ultimatum as the player, and whomever you choose will be the Primary LI. For a Primary LI to lose their tier, there must be another LI to take their place. There will be multiple opportunities to switch between Primary LIs. Alas, the more you switch between LIs, the more drama-filled your play-through will become, while if you stay faithful the entire time, your experience will be more akin to a wholesome, romantic experience with little drama.
In the case of the throuple path, Glade must be your Primary LI when you get the option to become a 'throuple' while Lorelei must either be a Secondary LI.
That's the gist of how Love Paths work. I didn't include all the complications with the Allegiance Paths as that would make it a little confusing for everyone. If you have any queries, I'll be happy to answer them as long as they don't spoil anything.