Polyamory is different in theory than in practice.
We opened our marriage when I fell in love with another man. Poly was the best alternative for us, the other options being stop loving my boyfriend or get a divorce.
We agreed that this opened the door for my husband to explore new relationships as well. IN THEORY this seemed like a good idea, fair, etc.
In reality, when he did find a girl and they started a relationship about a month ago, I was crushed. It's still new to me, my emotions are all over the place, some days I feel like I'm going crazy with jealousy and fear and grief and remorse.
I fell in love, and THEN we made a poly agreement.... but my husband's progression happened in the opposite order (well, he hasn't "fallen in love" with her -- but she has, with him, and I wonder if it's only a matter of time before he falls for her, too). I wasn't looking; but after we made our agreement, my husband was. My husband, who never so much as LOOKED at another woman in our entire 12 years of marriage. I thought I'd be ok with it. Maybe I will be, in time, but at the beginning, it is terribly rough (it was rough on my husband too -- I'm just now experiencing the other side).
Poly is not easy. If you've got a good solid marriage to begin with, it's better, but it will still rock the hell out of it. As compared to monogamy, the highs are much higher, but the lows are equally lower. If you love roller coasters, welcome aboard! But for me, there have been LOTS of times where I've thought, "STOP THE RIDE, I WANT TO GET OFF!" and well, once you're in motion, it is just not that simple. Glad you're here. Look before you leap!