The reason why many people get disappointed by others is because they have too many expectations. Have none.
Even if you have family ties or share a work commitment with someone, understand that no one owes you anything, and everything he or she gives to you, time, efforts or affection, are gifts that can be withdrawn at anytime.
If you begrudge anyone for taking away what was theirs to give, in the first place, you do yourself no service at all. It was a gift for a time, and your feelings of entitlement aren’t warranted.