Originally Posted by BigGuy
Sky, the answer to your question is... "it depends".
One-night stands don't fall under the poly umbrella technically speaking. It implies a random hook-up with no emotions involved, where emotional connection is one of the key components that define the polyamory concept.
My impression of the intent of your agreement is for one partner to have some protection if the other is about to bring extra drama into the relationship dynamic by sticking dick in crazy or vice versa.
Your problem is that this really isn't a one-night stand.
She's been talking to him, but you haven't really indicated if she has an emotional connection with him, or if this is purely a physical encounter. If its just sex, then I would say this situation isn't covered by your agreement. Like SourGirl says, (if I'm reading her right) if it's just sex, its a non issue because he wont ever be part of the picture.
Now, if she does have an emotional connection or there is a substantial possibility that an emotional connection could develop, then I would say your agreement does apply in this situation.
In which case, your problem isn't him. Its her.
You are going to have to decide, if she's willing to throw agreements out the window whenever NRE strikes, whether or not the benefit you receive from relationship is worth the additional grief she generates.
I always sigh a little inside when I see the whole ONS = no emotions. That's not true at all, otherwise you might as well just masturbate. Excitement of someone new is an emotion, the curiosity of a warm new body is an emotion. ONS does not imply zero emotion, it implies (well in fact it explicitly states) that it will only be for one night. There is also nothing random about it, since ONS will only happen when there's some form of chemistry between two people.
Like you say though, this problem is unrelated to ONS. End of the day, the guy has clearly said that he's not into poly, and is specifically making plans for after your relationship, major red flags to me. You need to have a word with your girlfriend about why she's planning on going to see him, because to me it just looks like a drama-explosion waiting to happen.