Sometimes the break-up happens first, before the next partner is 'found,' as well. I don't know exactly where my saturation limit lies, but I'm starting to believe I might be at it, simply because of the type of men I become attached to. I have a husband of 18 years, who for most of our relationship has been rather independent, as have I. My bf and I have been together a year and a half, a year of that with a shared gf. She was very time demanding for me (which I did not mind), while he was not. (I wanted him to be more so.) When she broke up with us, he and I gravitated toward spending a lot more time together, and that shift was something we both enjoyed, and something he got used to.
I met someone else about five weeks ago. While I will admit there is most certainly an NRE-factor in there, I do very much believe this is a person that I mesh with in a 1001 ways. He is also a very high-time demand person and thus, I'm now in three romantic relationships - 2 of which are high time demand and one which is medium, but probably wants more. and I have work/kids/etc., as well.
I already know my bf is feeling the difference from me spending time with this new man. I know my husband is feeling the difference of me having two others again.
I cannot imagine trying to add anyone else to my fold.
But I've also never 'looked.' I didn't feel like I was missing anything when I was with my bf and husband only. I wasn't out there tindering or whatever else people use these days. I stumbled nearly by accident across the new connection, and when something FEELS right, I have to see it out. That was, I believe, part of the source of my unhappiness before.
I don't want to have to give up anyone already in my life, however. So there is that awareness there that I am likely 'maxed out.' At the moment, all three of them have only me. (Husband has never added another relationship since we opened, bf hasn't had another one since gf, and new man just ended things with his gf, just after meeting me, for non-related to me reasons.) I am their sole focus in that area.
If they all ended up with another partner, would that free up time for me to meet someone else? It's hard to say.
I hope that helps a bit with your questions/comments.