I had originally spent about 30 minutes typing out the whole situation, but my computer spazzed out and erased it all
Frustration got the better of me and I went for a shorter post. But since you asked, here goes the whole shebang:
I met her early this year in my art class and our friendship grew very quickly because we have similar pasts and understand a lot about each other that most people don't. We are very much best friends and care for each other deeply. Being that we're both bi-sexual, and I'm submissive while she's dominate -which caused a slight rift in their sex life occasionally because he's also dominate. She's willing to be submissive for him, but he doesn't do the same for her- we discussed the possibility of us being intimate but she didn't feel right about it without her guy being involved(who lives in another state). He and I spoke a few times online and on the phone if I was with her when he called and got along pretty well, so we had a little bit of familiarity with each other before he came down for his yearly month-long visit. When we met in person there was an instant connection and attraction to each other.
The night he arrived I ended up staying at her place with them because we had made plans for the following day. Given she had a house full of guests we all shared her bed(it's been a normal thing for me to sleep in her bed with her when I stay over, so it wasn't a big deal to me.) At first I was giving them their space and apologized in advance if I ended up cuddling him in the middle of the night and they responded with and invitation to go ahead and cuddle with them. So, I did. The next day we were all still cuddling and talking about how nice it was and I casually(and playfully) mentioned polyamory. We discussed what it was and our views and things on it, but not whether we actually wanted to do it.
The day went on and since our plans weren't until that evening we all just stayed in her room talking and cuddling. Our discussion led to talking about me being intimate with him and she said that she didn't care if we did anything. He and I didn't do anything until that night after we got back from our plans. We started kissing and touching and things were progressing, so he stopped to ask if she wanted to join us and if she was still OK with it. She declined to join but said we could go ahead, so we continued. But a few minutes later she abruptly leaves the room leaving us worried and confused. He went to talk to her and returned about 30 minutes later with the news that we weren't going to be picking up where we left off, ever. I had assumed as much before he got back so I was just worried about my friendship with her. She told him to let me know that we were still best friends but it would take at least a few days to get back to normal.
So, we all tried to go to sleep. It was awkward since we still had to sleep in the same bed, but I laid at the foot to avoid as much awkward as possible. She eventually asked if I was OK and came to lay with me and we talked and made up. The next day we spent cuddling again until I had to leave.
After all that I couldn't get them off my mind. I missed them both terribly and kept wondering if a poly relationship could ever work between the three of us. The next night, I couldn't bare to keep it to myself anymore, so I wrote her a long email explaining my thoughts and feelings and waited for a reply. When she replied, I was ecstatic. They had stayed up until 6 that morning discussing what I had on my mind. She had come to the conclusion that she was jealous of the two of us being intimate without her, not just jealous that her friend was intimate with her boyfriend. They had intended to discuss a triad relationship the next time they saw me in person, but since I opened the can, the worms spilled.
So for the last two weeks, I've been their girlfriend. The first few days were so easy and everything was so smooth, I didn't expect to run into any issues when I spent time with them in person again. They're being very patient and understanding with me about the insecurities I've expressed since this is their first real follow-through of anything with a third. They had considered a couple of other girls and one guy before me over the years, but for one reason or another, they didn't work out. I'm the first to be officially deemed 'girlfriend'.
I hope this all helps and isn't too much to read.. =)