I don’t know if it’s right or wrong. It just is. You feel what you feel. Anger certainly seems understandable in your situation, but I think you have to give the guy a little leeway. Can you imagine what it must feel like to find out you have cancer? It must put your life into a tailspin. I’m sure it’s scary and devastating and confusing. Maybe he thought he was doing the right thing to break up with you, then after a month he either got a better diagnosis or got lonely but was too ashamed to call you back. Or maybe he thought being alone was the right thing to do, then he met someone who made him feel otherwise.
Could he have handled it better? Probably. In a normal situation, I would share your righteous anger, but this is not a normal situation. As extenuating circumstances go, life-threatening disease is a big one. Yes, this could have been an elaborate plan to dump you, or he could have simply panicked and did something impulsive, then felt too guilty to undo it. Either way, what’s done is done, and you need to let it go. The guy has cancer and he made a mistake. I say give him a pass.
Thanks for the question.