smoothing the bumps
It is morning here and I haven't got a lot of time so I'll try and give a little reply but will have another look at this tonight. I've re read your comments but I still find it quite difficult to get a handle on everything that is going on for you.
From your last comment you say that you have communicated how you're feeling to O and he has been supportive, so that's great.
When I met Z I had not had a well functioning poly relationship because my husband couldn't handle it. When the marriage ended and I met Z and he had this other relationship already existing it didn't worry me. I thought, great, this is will allow me to also explore polyamory. But the reality was a whole lot different.
The more I fell in love with Z the less I wanted anyone else and the more I craved a one on one relationship with him. It was suddenly terrifying to have this level of feeling for someone who also loved someone else. Like you I started wondering who the hell I really was and what the hell I was doing.
It still worries me because when I met Z he was also just out of a marriage where he hadn't been honest about his love for J. His love for her has grown during our time to together and I worry about where it will end up. But love has no guarantees. I believe in our honesty and I try to trust the commitments he has made to me. That's really all anyone can do, even in mono relationship.
Hope this is somewhat helpful