Helping a friend with AML

I would be really grateful for any opinions on my current predicament.

My best friend has confided in me and only one other, that she is undergoing chemotherapy for AML. She has a husband and four kids but she's not told him. Her reason being that he will crack up and she can't cope with supporting him and going through the illness herself.

I've said I'm there for her and I do understand her point of view but surely she should tell him? He thinks she is just working long hours when she is late home but really she is at hospital.

I don't know what to do for the best.