She hasn't told him, Marlon "The arms" dingle only found out cause he got his usually bit between the teeth and wouldn't leave it alone, as he does repeatedly when the story requires.
A lot of people have mentioned before in this forum, that it is strange that apart from a few hot flushes she shows no signs, even though she is so close to then end. Not sure they are portraying this correctly, then I don't know much about cancer or the effects. She has a scan on Monday, maybe she just has constipation and it is all a big mistake.
I do think she is wrong to lead that Ross guy on so to speak, but if I was close to the end I would probably be trying to get it on with some women before I was unable I suppose. It's all a bit strange