I don't mind answering these kind of questions, but I do want to be transparent. Since my focus has been on preserving Viv's art and work rather than learning about her personal life and relationships, this isn't my best subject. I tend to just absorb this information randomly along the way, and since I wasn't around at the time this stuff happened, I won't claim to be an expert.
I also want to make it clear that I don't actually consider it any of my business and don't feel it's my place to speculate or make assumptions about her relationships.
The best I can do is give you what random information I've come across that I feel is relevant to the fandom. So, I do advise you to take this with a grain of salt where sources aren't directly provided and I'm always open to being corrected if I'm wrong about something.
Viv and Faust were close friends in the 2010s and started RPing with Tyco and Angel in 2013 which is the year of Angel's creation. In my opinion, it's likely these RPs were very helpful and pivotal to the development of his character. It's sort of what RP is good for; getting to know your character by throwing them up against situations and characters that don't come from your own mind. So, in that sense, I do think Faust had some indirect impact on Angel Dust's development through the RPs.
I'm unsure when exactly the RPs ended, but I'm under the impression they ended a good amount of time prior to the development of the pilot.
Since Faust was Viv's friend, he wound up working on Hazbin Hotel during the pilot era. And these RPs could be found/seen by new and old fans alike, leading many to assume Tyco would be part of Hazbin Hotel. Eventually, Viv had to make a post clarifying Tyco was Faust's character and would not have anything to do with Hazbin Hotel.
The RPs were never meant to be canon as far as I can tell. My belief is they were simply good fun between good friends with no thought of permanency or impact on a larger fandom they frankly could not have seen coming.
In addition to being an illustrator for the pilot, Faust was placed in charge of the creation of the official Hazbin Hotel comics. He began to stream while working on official Hazbin material. During these streams, people would ask him questions and he would give answers that weren't always sanctioned by Viv.
From what I understand, during this time, Viv was so busy that she wasn't able to stream and provide content for her audience as much as she had before, so they latched onto these Faust streams as a source for official information. This is where a lot of pilot era fanon trends arose.
But none of this information was canon at the time. Faust may have had some insights that weren't available to the public but what had roots in that insight and what he pulled out of thin air during stream could not be determined.
In the end, all information garnered from the streams had to be denounced. So, any information from that source cannot be considered canon until it appears on screen.
In my opinion, I think Faust was working very hard and doing what he could to provide the audience with something to chew on while they were trying to get everything going for the pilot. I don't think there was any malicious intent or purposeful misinformation on his part. Just starved fans running wild with anything they could claw out of the crew.
He worked on the two official comics that were completed, but was also in the process of working on one featuring Vaggie, Charlie, and Helsa Von Eldritch. It was meant to be set in high school where Charlie and Vaggie had met for the first time. Obviously, this is no longer anywhere near canon and was never finished.
As far as the "falling out" between Viv and Faust goes - if one occurred - I'm in the dark. I don't know what happened and I don't consider it worth the research to find out. (That's time taken away from archiving the art.) But I do know that they were very civil to each other in the posts I did find about Faust leaving the project. Viv wished him luck on his next project and Faust responded professionally. Faust also gave several other reasons why he left which included moving and burnout.
While I found no posts that showcased frustration or anger at Viv*, there were posts about burnout and Faust had a hard time convincing fans of the show to stop emailing him. I've always assumed that if anything happened between Viv and Faust on a personal or professional level, it was settled privately.
The only important thing to know now is that Faust no longer works with Viv and past information derived from his streams cannot be considered canon.
*I'm not saying they don't exist, simply that I never found any. But I also never went out of my way to find these sorts of posts.
