It's really imortant to first allow yourself to be upset and to feel all your feelings. Let it all out, and get in touch with part of you that is so hurt. Lovingly and without judgment, because all feelings are valid.
And then when you've come out the other side, downgrade the offending relationships accordingly.
I truly believe most people are good and kind. But when someone shows me they are less than I desire in my life, I downgrade them - or remove them completely. I'm pretty ruthless that way, because if my life is full of flakes, 'takers' and people I don't vibe with, there's no room for the reliable, reciprocal and suitable people.
I learned this when I cut out everyone who had any contact whatsoever with the abusive ex. It was a removal of trash that had been cluttering up my life, and I was left with 3 friends, my ex-husband, several acquaintances and my family. Those acquaintances soon became good friends, and they introduced me to more good people, who weren't flaky or morally questonable.
Natalie Lue is great on this, with her 'circles of trust' - and her whole website is great for all sorts of relationships: https://www.baggagereclaim.co.uk/circle-of-trust-discernment/
Disappointment can only happen when you have expectations, and often we project our own good qualities onto others, and so expect them to act as we would. Whereas really we need to allow people to unfold, and only expect from them what they have a proven track record of being able to give.
When you are able to deeply know and accept that people's behaviour is about them not you, then you can let people go, understanding that you aren't losing anything, because you didn't have a true close friendship in the first place. You are just opening a door for one of the very many great people in this world to walk in.