my experience with poly thus far has brought all my old insecurities and some new ones, but I guess you have to deal with them sometime. Sometimes, I feel like if some one is not at that moment showing me affection and giving me attention then I think they have stopped caring or are angry at me. So being left out is definitely one that makes me feel insecure. Also, I tend to have a lot of ups and downs so I feel insecure sometimes that no one will want to have to deal with my sadness or things like that. I have so many insecurities that I'm insecure about them!
But I am glad that I'm able to see them and then try to really get to the root of them so I can someday unlearn them.