I did end up having to go way back to the beginning and start his route over using the guide but I believe that was a bug.
I was trying to pursue him but I noticed that when I got the scenes where he went to Germany and came back and took off again, that it skipped the scenes from "Paranoid" to "Guitar Pick". Needless to say I was confused when Lukas showed up. But the last time Faust showed up in game was when they left to go do whatever right after they came back ( he was "friends" with Robin because I wasn't even given the opportunity to choose) and never came back. I played through 6 months and checked the band meeting, did gigs, checked the shopping and band equipment screens to see if I was missing the trigger, and nothing. I checked on various days so it wasn't the same day problem.