Side note: When I covered this on Youtube, I did say he "either got fired, went off the deep end, or something fucked up happened and he wasn't a detective anymore". So I called it on Youtube, just not here.
But yeah, poor Sebastian was drummed out of his profession. That was the last thing that he loved and they took that from him. Geez... So he's lost his family, friends, and career all the things that tethered him to reality. No wonder he's at "his lowest point". As I previously stated, it wasn't like he had a lot going for him when we first met him in the original game, now he's just a full on poor lost soul. I guess it's little wonder when Juli approaches him he just sorta goes off to do Mobius's bidding, cause really at this point, what does he have left to lose? Man... That's really rough.
I had more to say on this, but I have to get ready for errands and then head off to music lessons. But this is the info via Bethesda's website that I saw. This is going to be depressing in parts I'm sure.