"I opened up to you" means "I told you many deeply personal things." Implicit but not said: "I expected you to empathize and give me emotional support." "...you judged me" means "You criticized me in a cold way." For example, imagine this conversation: A: "You look a little bit down. What's the matter?" (A asked B for information. A invited B to "open up" when it was clear that B was unhappy about something.) B: "Oh, I don't know what to do. I've been such a fool. He said he had an investment that was certain to double my money in six weeks, and I gave him everything in my bank account, and that was three months ago and he won't even answer my phone calls." (B opened up to A. B gave A embarrassing information). A: "Well, you certainly were a fool and it serves you right for doing such an idiotic thing." (A judged B, coldly and harshly). B: "I opened up to you, and you judged me! B probably hoped that A would say "Don't feel too bad, it could have happened to anyone, he's a very plausible guy and he's cheated dozens of people."

It means "I was honest with you and talked about myself and my feelings and you expressed a negative opinion about me."

This means that the person spoke from their heart and was judged. They shared intimate details. The other person judged them while they were vulnerable.