Well, first of all, my husband and I have elected to only see other people together, so that helps, although I do have another life partner who lives far away now, and that I have strictly an emotional relationship with at this point. But because it's all above board, my husband James considers my other partner Nat as an extended member of our family.
Next is that it's entirely possible to love more than one person at a time and to cultivate active relationships with more than one person at a time. One doesn't fade into roomate status just because there is someone else that you care about or love. This is what I mean when I say it's a very different relationship style.
I know of plenty of people who either live alone and have multiple partners or who live with one and see other people separately. Each relationship has it's own characteristics and elements to it, so they interface with different facets of the individual.
I've written quite a bit about polyamory, so I'm linking you a couple of stories that I hope will answer some of your questions.
Edit: there was just a thread about poly-saturation in my local Facebook group. Most people agreed that three partners was their limit although some said they couldn’t handle more than two, however all of this depends both on the people involved as well as the nature of the relationships. Are the other people spouse equivalents or are they more like boyfriends/girlfriends? It also depends on other circumstances like currently raising young children.
