I have to agree that the endings are really depressing and there isn't even a bittersweetness in them. I spent a lot of time, trying to figure out to heal our mentors or some sort of calm ending that doesn't lead to destruction or a broken guy. While I'm aware about the genre Drama and Psychological, I felt like the Markus Special Ending was - as a friend agrees - kind of lazy? Like an easy way to weasel out why things happened and why the choices had the effect they had. I felt like the real choices that mattered were the ones which faction we choose.
Ending spoilers and basically repeating what former poster said
The common endings are 1. If you get killed by a certain sewer dweller (you can avoid this by running away or as Mavvar you can survive by fighting back), and 2. If you're not high enough with a faction and get killed after announcement (this was also a huge bug in the earlier version)
The most endings for the guys are obvious: The faction you choose at the end - Saorise, Randal or Andrei. Making up three endings for each guy. Randal has one more with your own rebellion which you can achieve by deciding to make your own house (balance your reputation above 50 for each house, convince Randal to join you, Markus will mention that you have to infiltrate the houses... I suggest if you have problems with one house to help Andrei, so you meet Morgan who offers you to boost your reputation with one house in exchange to introduce her to Andrei. Figure out the rest.)
Then we have the romance/friendship endings for Heath and Randal (technically his faction ending). Easy as said, romance them. Markus will go away no matter what.
Finally the three special endings, which you can get by taking the red choices - to see them you have to be the same house as your mentor. Prepare to be shocked, cry or well, disappointed.
Endings spoilers end
All in all it was a great game but as many other players I share the same empty feeling after spending over 20+ hours on the game and waiting so long for its release. I also tried to figure out what the devs tried to convey with the hidden messages (like to try investigate on the texts you see in the backgrounds or CGs (Randals biker jacket saying in Latin "The world wants to betrayed." or something) and endings names of the guys (John 1.5 for example, a bible verse) as well the song playlists you unlock once you acquire a special ending) but I wracked my brain with the choices already.