Pierre was born in dysfunctional family, as well as surrounded by death at a young age. He lived with his mother at first, who was neglectful and abusive, and eventually his grandparents began taking care of him (who lived in a different country). This was a peaceful time and he was happy, but they passed away when he was around 12 and he was sent to the orphanage since the whereabouts of his mother were unknown but likely dead as well.
At the orphanage and school he was welcomed and well liked, however the scar of his upbringing was already there and didn't know how to heal.
Most people would describe him as well-mannered, calm and most importantly, very dependable young man, however inside, he felt detached from everything, nothing felt real. This is because after experiencing abandonment in the form of death he closed off his heart, and also his contradicting feelings (like missing his mother yet she was abusive) left him confused and opted to not feel at all.
Basically his "calm and dependable" exterior came from shutting down his feelings due to fear of getting attached to something he would later lose, as he was never able to understand the pain he felt at such young age, and excelling in things was a way to fill his "void".
He would get along with everyone, and everyone thought highly of him, but would never get a close relationship with anyone. Upon entering the orphanage which was catholic, he was introduced to this religion to which he devoted deeply as he felt like God would be the thing that would help him relieve his pain. He became very obsessive with the idea doing "the right thing" and being a "good person" because in a way, he felt that would heal him and make him feel fulfilled in life.
Thus what everyone saw as a nice, dependable, admirable person inside he felt a extreme loneliness, and a unbearable feeling of derealization.
In his last year of school, as well as last year in the orphanage, he met Deneb. Although opposed in many things, it was in such a away that they complemented each other and got along pretty well. Deneb was quick to start having feelings but Pierre was not so sure. As much as there was a small voice in him saying he wanted to be with him, he had too much baggage that was left unattended and while beginning to feel was nice, but it triggered so much.
He likely lost his sanity many years time ago and the only thing keeping his mind together was a veil of apathy, but once that veil was gone there was no turning back. So, one day he ran away and disappeared.
