Hi Pandora. I haven't read anyone else's response, so excuse me for the repeats if there are any.
I think that perhaps he just couldn't get it all together to do the poly thing with you. Sucks I know, but really, it seems to me that perhaps he couldn't balance it all and he decided it was better he spent all of his energy on his wife because she is the one he is struggling with. Maybe he found that he was getting too into you and had some guilt around that and found his emotions were being diverted from her or maybe he wasn't interested in you enough to warrant continuing or maybe he isn't in touch with his emotions enough to be able to handle anyone else's or maybe he just found it all too over whelming or didn't know how to be honest even if he had good intentions... being honest is a skill that needs practice. It can be hard when the feelings behind honesty are raw and negative. It becomes really hard to be honest when one is feeling like that sometimes.
I hope you get some idea as time passes. It sucks that he left you out of the loop. He might of thought he would wait and see if things changed, or was waiting for a moment.... or.... we could go on for ever theorizing really but really he is the one that knows and hasn't told you.
sorry you are hurting,
hugs to you.....