If an upset stays with you, it builds into a resentment. A resentment is a fundamental disagreement with the nature of a reality. This could be about a person's way of being. Even though they may do things that are outright upsetting, the resentment lives in you and it is you who is responsible for resolving it. They may or may not change as a result of you resolving the resentment. However, if you don't do any work to resolve your part of the pattern, that leaves 50% of the pattern intact.
It is especially difficult to bring your resentment to the person you are resenting. Odds are that they are already aware that you are resenting them so they may be ultra sensitive to any charge of judgment that you bring.
It takes immense skill and mindfulness to bring your resentment to a person you are resenting in a non-judgmental way and, even if you do this perfectly, they may still get upset.
You can throw out any notion that there is some magical way to bring it to them that will avoid all pain.
What you can do is learn to empathize. You can tell them about your hurt and empathize with their reaction.
"I imagine this may be really hard to hear."
Then breathe and stay in connection to yourself. Whatever they choose to do with the resentment is up to them and it will inform your next move. You are not obligated to fix their feelings, follow them around, or mask how you feel.
Stay with what's true.