Co-author of the upcoming (and funded Kickstarter!) book More than Two, Eve Rickert recently published an article online that I can't find anymore* wherein she details a few mis-steps that poly-n00bs tend to make. One of the things that she talked about is that your first few forays into non-monogamy aren't going to go how you think. Some things are going to crop up that you didn't know were issues, other things that you thought would be issues aren't going to bother you at all; most importantly, your heart is going to expand Grinch-style, and I think people being unprepared for that reality is at the root of the "Terrible Poly Story" that every veteran of non-monogamy has heard as an objection to their relationship-style.
I've seen a lot of people go from "this is a great idea!" to "this was a terrible experience!", or "we're trying this to save our marriage" to "non-monogamy broke my marriage" because sometimes when you just run thru a dungeon without looking you get eaten by a purple worm**. A lot of these people who run into this will say that they read all of the books, they thought and talked and wrote and everythinged*** on the subject of non-monogamy and polyamory in specific, but things still exploded in their faces.
That's because things aren't going to go how you think when you first start into polyamory. Some people are lucky. Some people are more insightful that the rest of us and know all the pitfalls they're about to avoid, but most of us aren't that wise. Unfortunately, it's not possible to predict the future, and even if you could predict it, affecting it is another skill entirely, no matter what the teevee says. But, because there are no foreseeable problems on the horizon, we get cocky about the way situations are going to unfold as we open up an existing monogamous relationship into being polyamorous. This is the downfall of even the healthiest couples (and yes, I know, I'm being annoyingly couple-centric in this topic so far, I'm sorry*') runs into roadblocks that can become insurmountable.
Singlish people who start out down the non-monogamy road encounter problems too. You say, "I'm no longer interested in monogamy", then you meet someone, and you tell them. But you end up being effectively monogamous with that person for several years, because of reasons. Or you meet person after person who says "yeah, I'm into that" at first, then turns out to not even sort of be into non-monogamy, they just think you're hot and want to touch your boobs. I could probably go on, but it's really not necessary.
My entire point here is that relationships are unpredictable, because people aren't rational. When you declare yourself rational, you start to overlook things. Small things. That thing that your partner said that really bothered you, but you're ignoring because you'd rather think of your New Shiny. A twinge of jealousy. A goodnight text. Subtle passive-aggressive behavior. Tiny insults. LIfe's situations are new, and you're rational, and having an emotional respose to a forgotten text, or a perceived slight isn't rational. Let it go, you say, it's not important. Most of this is good.
But, pretty soon it's really important and you're suffering and you don't know what to do because the rational thing isn't working anymore. You're having an emotional reation to something you said was unimportant, weeping on the floor for no reason. Or not. Some people shut down here. Ultimately, the only way to prepare yourself for the roadblocks in this uncharted territory is to admit that beginning polyamory is uncharted for you, and to pay very close attention to your emotional reactions to things.
Also, don't blame your new partners for problems in your existing relationships. That's called being a dick, and if you keep doing that, NO ONE WILL FUCK YOU EVER AGAIN. If you're using non-monogamy to try to fix the problems in your monogamous relationship, that relationship is going to end and it's going to suck really hard for everyone you date and everyone your partner dates*''. Fucking fix that shit before you even THINK of developing new emotional entanglements.
After that, maybe give it a year. What a year? Yeah. A year. The transition from monogamy to non-monogamy is one of the biggest changes you can make in a relationship, and pulling new people in too soon is a bad idea. Don't take my word for it, ask your poly friends about their Poly Horror Stories. And if you don't have any poly friends yet, it's probably not time to start dating yet. Just an idea.
Something else that isn't going to go how you expect, is that not everyone you meet is going to have the same poly-style as you - especially if you don't have a style yet. Trying to conform your style to theirs can work, but usually it's just going to explode. But, if you have a history of relating to people in an intense way, the person who is much more casual with their sexual attention is probably going to break your heart*''', even if they don't mean to. True story.
Know yourself. Don't get cocky. Listen to your emotions, and please make sure you're going to extra measures to make sure your existing partner is heard. Also, if your existing relationship isn't good, don't think that adding more people is going to make it better. It won't.
*Full disclosure, I didn't look that hard.
*Continuing the theme for this entry's footnotes: yes, I watched the D&D episode of Community then mainlined season 6 of The Guild tonight. You knew I was a nerd when you started reading my blog.
***I'm sorry, it's a verb now. Not actually sorry.
*'Actually sorry. Keep reading.
*''After being dumped several times because "things aren't going well in my marriage and I need to focus on that" I've stopped dating people who are new to polyamory because they think it's the solution to their marital problems. It's not. Counseling is.
*'''Another person who gets set into the "not now" category, is the one who doesn't have their own poly figured out. I know, it's not fair, but I'm not the gal you cut your poly teeth on. This isn't a 100-level class.