step parenting

I am writing this while perched on my chair that is lowered to 10" from the ground. I am waist deep in files and folders, transferring my once '2 floors on trendy Queen St and now downgraded to part of the basement rec room' office.
My step son, 32, moved in Dec 18. He came to Toronto just before Xmas. Ironically this was probably the final Xmas Chris' family would be spending together- his Dad would be put into a nursing home shortly after xmas. Bryn chose to be in Toronto to spend his xmas with - what I can only assume is what he perceives as - his family.
His mother Trish has been the driving force in his life. She is dominating, egotistical and must own the room/emotion/feeling/argument in every location she positions herself. It was embarrassing for Chris and must be for her current husband. She has derided him in public, in front of us.
That is the tableau from which Bryn was raised. When Chris started his affair with Kate, it lasted a year before he left Trish. He says they even had dinner in the same restaurant and Trish pretended not to notice (they were still married at the time).
Chris' mother told us of how she lugged Bryn to her place and whaled about the unfairness of it all, but that Bryn was her little man and would always be her protector. The child was destined from age 3.
It was made clear to me that Bryn would never be my child. I have no idea what was drilled into him when Chris and I got together, but our one blow out when Chris, Bryn and I were on vacation when he was about 10 reinforced Bryn's position. "You're not my mother" he screamed. I told him I was not his mother, and I knew that. But I was his father's partner.
I spent much time encouraging Chris to engage with his son. He had virtually left that relationship behind when he left for Kate. She hated kids, she damaged Bryn, Chris fell in with it. Appalling. No wonder his son gravitated so magnetically to his mother. And she brought her new relationship into a new chance for Lee. He had abandoned his son, and now had a chance at redemption. He became Bryn's father. I am sure that many of their friends don't know that he isn't Bryn's father.
Trish signs her Xmas cards 'To our wonderful son, Love Mom and Dad'. That's not too fine a point, is it?
I read a journal I'd written when Bryn was in high school. It predicted that he would end up in a career facilitated by his mother. And guess what - he has. It took him 13 years to get a Bachelor's degree, he finally found his calling to become a nurse. And now he's working for a friend of Trish's in the massage therapy association.
It just pushes me and mt relevance further and further away. I suggested to him when Chris had his stroke that he become a nurse. He says he has no memory of that.
I am so nothing.

And now I've moved my office- my life for the past 20 years- into this little hole in the basement.
I feel like a nothing.