I did vote, although out of my three partners, only my husband is currently operating under the primary/secondary models, as far as I understand, both my other partners just consider people "partners"
Are you kept completely isolated, and a secret from, from their friends, family, neighbors, co-workers, or anyone else?
Brian, my partner of 2.5 years, is not out as poly to his family, and they live in another country. When his mother visited this year, I did not meet her, neither did his other partner of 7 years. He is really private and just thinks nothing is their business. His soon to be ex-wife didn't want to be friends with me, and I respected that, but it did mean there wasn't meshing of space on that level, no board game nights or movies. Now that he and his wife have separated. I have recently been invited a couple times to events where coworkers would be. In general hs is not interested in his coworkers knowing his personal business.
Greg, who I have been with less than a year, is not out to one sibling, but not to his parents, though it looks like he will be not too far in the future, and he is looking forward to introduce both me and his other partner to them. He has recently become more out at work, which is nice, as my husband works at the same company, and my husband is very out as poly. He's invited me to a work type party but we didn't end up going.
I would be open to being totally a secret to family/coworkers in a casual relationship, but never to friends/other partners.
Is your relationship known to some of the people in your partner's life? Is there some integration, but some people from whom your partner chooses to keep your relationship secret (or private, if you prefer?)
Don't think there is anything to say that I didn't say in the former answer - both of my other partners are either all out in places, or not out, neither of them introduce partner A around, but not partner B, or vice versa. My relationships with my partners are known to my friends and family that I care enough to have in my life, my husband feels free to reference to his friends and coworkers when I have plans with my boyfriends.
Or are your partner's friends, family, neighbors, and co-workers as much a part of your life as they would be if you were a spouse?
No. I don't have to talk to their neighbors because I don't live with them. I don't have to go to holidays if I don't want to. I don't have to go to work events if I don't want to. I feel more of an obligation to do some of these things with my husband.
That said - Greg is making an attempt to make me a part of his life in a way that makes it possible for me to spend time with his other partners and friends. I *may* have them be as much a part of my life as I would if they were friends and partners of my spouse, my husband doesn't mind hosting people here, so at some point a nice general extended family dynamic might be taking over. My goal in general is to spend time with people I like, and not to be with people I don't have stuff in common with, and that goes the same for your friends, partners and coworkers if I'm married to you or just seeing you once a month.
If your partner, or the two of you jointly, decide to keep your relationship private from some or all, what are your reasons?
As I mentioned, both of my partners aren't all out everywhere. I respect this, and will refrain from PDA or mentioning being in a relationship with them as needed. Nevertheless, this has made me realize that I am not really interested in being involved with people who are not fully out if they want to have me around people they care about, especially if they are close with their family. I don't have any interest in hanging out in a group "pretending" I am just a friend, and luckily I haven't had to do that.
Happiness will never come to those who fail to appreciate what they already have.