How to help a sick friend

Please help me. I need some advice. I have a very dear friend who is a survivor of throat cancer. He was recently diagnosed with multiple myeloma and is going through some very extreme and rough treatments. I have always let him know that I’m here for him texting every day just sending love and support. Until recently he was very appreciative and even said how much it means to him and that he couldn’t do this without me. Now suddenly he’s become distant and annoyed with my trying to contact him calling me selfish and saying I’m stressing him out while he’s trying to get better. I know he’s mentally and physically exhausted. I’m heartbroken but the last thing I want is to put added stress on him. It’s so hard for me not to contact him but he says that’s what he wants. I’m so sad that he’s going through this alone but he clearly doesn’t want to talk about it. I’m so afraid he will take a turn for the worse or even die and there’s no way I would even know. It’s so frustrating being pushed away and being told I’m selfish when all I’ve ever done is been there. I’m trying to be understanding and not take it personally because I know it’s the cancer and all the pain he’s in talking but it’s difficult. What can I do? Is this a common reaction that people have? Any advice?