This depends on the seriousness of the relationships to me. I have on all of my dating profiles that I am in a romantic relationship and open to partners in addition to that. Currently they say that I’m monogamishly dating a poly person (just like this blog does). So, it’s important to me to be transparent with new people. At which point I tell JJ that I am interacting with someone new isn’t super important to me; I’m fine deferring to what he’d prefer. It is only important to me that JJ meet any other partners of mine when those partners feel established in some sense, because unlike him, most of the people that I go out with do not turn into partners in any significant sense of the word.
Regarding his other lovers, as they have all been very significant to his life, it is important to me that I meet them. I do not like that I never met the person his most recent outside relationship was with, and I think that that factored into making me less attuned to her needs/interests/feelings and aware of their relationship as a Relationship. It is an absolute requirement that we know about each other. I do not need us to be friends or hang out or all spend time together with any sort of regularity. In fact, I would in some ways prefer being spared group interaction, because I don’t really know what kind of relationship I’m supposed to develop with the partner of my partner. If there is some magical unexpected future in which the existence of such a person doesn’t make me uncomfortable, then maybe we could try to establish some sort of cordial/friendly relationship, but this seems unlikely to me. I strive to always be respectful of his other relationships, though, and to not unduly stress my preferences/feelings over his freedom within those relationships.