Ya, being betrayed is definately up there. Primary vulnerability? Close to it. I'd say that for me, and I don't really know if its e6 related or not, but being without a close support network is probably one of the scariest things I can imagine. Not like I can't be alone for extended periods of time.. I really enjoy my reading and cooking and music and hobbying.. but I have to have close people in my life to share things with. If I even go 1 day without being able to call up someone and blather on about random stuff I feel a bit disconnected. So i'd say it goes support group then betrayal then being caught off-guard. The last one depends on the situation, too. I like to have a general idea of how most things are going to go, and I really despise "pop-ins" from anyone thats not immediate circle.
I've been betrayed by both a friend (not such a good friend anymore) and a partner. Both times I was completely flabbergasted and extremely hurt. I typically deal with this by cutting my interaction off. I might fantasize about some things I could pull over them to seek vengeance, but I can never actually follow through with that kind of stuff. It honestly makes me feel sick, like spiritually sick, to consider moving the idea into action. This stems from a few things. First, I am already anxious and worrying about how someone else might retaliate (especially someone who knows me well as they might have some strong ammo) and 2nd, as a 6 I already have enough doubts in my charactor and past, I really don't like adding things to that list.
Anyhow, I think betrayal hurts the 6 so much because we already have a hard time trusting.. ourselves and others. When someone very close does this it is not only a let down, it causes us to question our own judgement in the future.. Atleast I tend to be this way.. too hard on myself for not catching that someone was capeable of doing X (even if no one else saw it coming either.)