Your third paragraph is something I have experienced too. I kind of make friends easily and would want to open up to them and this is because I am free and I tend to flow along making you a friend but somehow somewhere, I felt I shouldn't have opened up to people especially since there are some who would use those words against you,, It happened to me and I thought I expected them to keep my secret but it wasn´t so. I just have to get away from such friendships and remain who I am.
Though, we humans tend to expect high from others whereas we aren´t in any way up to the standard we set for them. I believe if we don´t want to keep getting disappointed every time, we should stop expecting too much from people because humans will be humans, not perfect and with flaws.
There's no way we cannot expect too much from people, it's embedded in us by default to hold people in estimable situations, hence even if we know we shouldn't expect a lot from them, we end up doing so and hence bear the regrets.
My circle is so thin nowadays, this is as a result of the experiences I've had in the past and even still having. I'm thinking we'd always find ourselves in the positions where we're disappointed because of expecting people to be up to par.
You are right. It's something we cannot do without. It's already in everyone especially when you expect people to fulfill their promises and they end up disappointing us. It's so sad though but we can't do anything about it.