So, an intro? I'm not completely new to polyamory; my wife and I are both bi, and have been poly since the start of our relationship, but only for same-sex relationships - we agreed to be exclusive opposite-sex partners. In practice, we've been pretty much exclusive partners for most of that time, too; neither us has had much time or energy to put into seeking other relationships.
Over the years the exclusion boundary has moved, to allow snogging, petting, and other activities, but until recently, genital-genital and oral-genital contact was off the table.
Or so I thought; it seems we took away different outcomes from the last conversation on that subject. This didn't matter until recently.
My wife's struck up a friendship with a guy which she'd like to take to the next level. It hasn't gone there yet: we've been negotiating boundaries and checkpoints, and the new friend doesn't even know her sentiments, and for all we know may not share them. (Though as I've pointed out, most men are not wired to turn down no-strings sex.) We've agreed that we both need to meet any potential partners before things go any further, and have even granted each other a veto ("Power of - cockblock! form of - veto!"), mostly in case one of us gets a negative vibe that the other doesn't.
Most of the time I feel OK with this, and in fact it's helped bring us closer together than we already were, but sometimes it scares me. For dumb reasons, because I know rationally that we're as solid as a very solid thing, and I really don't want to stand in the way of her getting what she wants, and she returns that sentiment, but it's new territory for us, and you never know quite what's going to happen.
So that's where I'm coming from...a sense of growth and curiosity tinged with a bit of fear and insecurity.