<human>: my best friend is at college in another state than me. this is her first year of college and she's never had a boyfriend before.

finally, she fell in love with this guy and they started dating. she was over the moon about it and really, really is infatuated with him.

at first, it was great, but then it got bad.

it's a textbook emotionally abusive relationship. he will treat her like shit - degrade her, manipulate her, control who her friends are, how she spends her time, make her feel trapped, freak the fuck out when she talks to other men. she frequently describes feeling helpless and that she has "no control." then, just when she tells us she is so miserable she can't take it anymore, he suddenly becomes an amazing boyfriend - loving, sweet, etc. this cycle continues over and over.

the kicker is that her boyfriend has cancer, and he frequently uses this to manipulate her. i have tried everything and gotten her to realize that she is stuck in a cycle, but she says (direct quote) that "there's nothing he could do to me that's more horrible than me leaving him when he's like this" (like this = going through chemo). she feels she cannot leave him because he is sick and always excuses his awful behavior with his sickness.

it's horrible that he has cancer, but it does not justify him emotionally abusing her and this horrible cycle that she is trapped in. how do i make her see this? i need to help my best friend. my heart is breaking for her and i am so far away. 

i am hoping she can use the summer break from school to cleanse herself of him. 

please: how do i convince her that it's okay to leave him, even though he has cancer?

Provide a brief overview of the text.
<bot>: friend is in an emotionally abusive relationship but won't leave her SO bc he has cancer. how do i convince her it's okay to leave?