Oh my word, people! Having a feeling is not in and itself wrong! It's just information your brain is giving you about your life and situation!
You don't need to feel bad because you're having a feeling even if someone else’s situation is obviously more important. You get to have your feelings! It may or may not be appropriate to like, act on that feeling with the other person, there's a thousand selfish acts, sure. But having the feeling itself isn't one of them!
So someone cancelled plans because someone died, and you feel sad or disappointed? Fair! Cancelled plans suck! You get to be sad and disappointed! Maybe don't go asking them for comfort, maybe go deal with it with other people or make other plans or do what you need to take care of yourself, or push past and take care of them.
But you get to feel it. It's still your brain saying “Hey, this was important to you! It sucks!”
Too many people in my life need to understand this.
Your emotions get to be independent of other people's. Entirely. They are YOURS. The things that go on inside your head are _yours_. You don't owe them to anyone, you don't have to change them for anyone. Your ideas, your feelings, everything. It’s all yours.
And then, when you take care of that and realize that they are in fact yours, you can much more wisely choose when and how to share them instead of being in constant conflict.