Ohhh, Robin, how I love your twisty questions!

I do hang out with multiple lovers (and loves) at the same time. Often in that situation everyone is just "family." Usually I'm good about keeping "touchy-feely" behavior in check, so as to not draw attention. But my lovers generally know and accept each other and their respective places in my life.

I also don't bring lovers home unless i sense that they'll be "family." Fuck-buddies don't have the same privelages... which may sound harsh, but I find that with some people, it's just better that way.

--M

For me, it's much easier to be the one whose other lovers are hanging out than to be one of the "other lovers" in this situation--I'm really shy anyway, and meeting new people tends to bring out a lot of my insecurities. This effect is doubled when the person has been intimate with someone that I care about-- I can go into some highly unhealthy "they're more attractive/smarter/sexier/cooler/whatever" thought processes, especially when "my" lover is being cuddly or affectionate with someone else.

I think the best way to ease into it is neutral ground or neutral activity-- going out for coffee, hanging out at a gathering where lots of folks are present, or playing a board game, for example. The best is when that person has a mutual interest with me other than the lover--a shared fandom or hobby that gives you something fun to talk about and get comfortable with the person. What has not worked for me in the past is "jumping right in" and meeting with the expectation of a threesome or going to a sex party together--but everyone's different. I find that if I connect with the person as a friend, insecurities tend to melt away, which is a really fantastic bonus to hanging out together and taking a "family" approach as opposed to "the other person" approach.

I'm a let's-make-peace person in most situations. If I am with multiple loves at once, I really want them to like each other and be able to be friendly, but I don't expect them to jump into bed together. I do tend to avoid big sloppy PDAs, and keep any touching, er, even and light. I wonder, though, that maybe my concerns about being "fair" to everyone are silly, and that I am missing out on more closeness. Perhaps I am underestimating the abilities of my companions to talk it out.

I know that the times that I've been a spoke (as opposed to hub), my feelings have varied tremendously. I always walk in to the first meeting with a little anxiety, but a determination to like this new person. I am always excited for the hub, and aware of their desire that things go smoothly, and that helps to remind me that my anxiety isn't so necessary. The hub is usually more anxious than I am!
Sometimes that takes care of it, sometimes it doesn't. I'll admit that there have been times that have been really uncomfortable, but I do my best to get through it politely, and just plan to talk it over later.
It has often happened that these first meetings have been held in _my_ home, so my duty is primarily to be kind to all of my guests and make them feel comfy. That helps me focus on something other than _my_ anxiety. However, it makes it harder to excuse myself if I've reached my limit in some way (tired, sick, or just out of sociability).

So, that covers vetting for new, possibly long-term people.

For short-term situations, forget it. It is great if everyone can be friendly, but if they can't, then I try not to worry about it. I just note that like some situations in grade school, separation is best. If someone is being a big wheezing brat, and I don't have to associate with them further, I don't. If I am the hub in that situation, that just tells me that this is, indeed, not destined to last.
In fact, even if I am otherwise really excited about this new spoke-person, that kind of rudeness will poison it for me. If it is a long-standing spoke-person that is behaving poorly, then it is time for a big talk to find out what is going on!

If I am the spoke in that situation, my refusal to put up with another spoke's snottiness sometimes makes the hub unhappy, and I am very willing to discuss it and give it another try if the hub really desires it (like if a new short-term person may become long-term), but if the other spoke is, again, a beast and doesn't seem to be able to behave, I'm out. Life is too short, and I am worth more than that.
It works out to: "Hub-person, you go on and enjoy yourself, but I don't relish the company of your new friend, so please be willing to accept that."

Ideally, we'd all like each other equally, and no one would have anxiety, but I haven't had much of that situation. That has only really been when all of us go into it assuming it will be no big deal. Maybe that is the key. Like-minded people can pull it off, and I think that is most common when no one is fearful.