Your friend isn't entirely alone. She obviously has a close friend who cares enough to ask for advice before advising her. She's got it tough, but "for better or worse" entails a lot. Just be sure if something happens you don't feel caught up in the middle. I can't help but admire your caring and support for her. That should be an advantage, let's see if she sees it.

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As to marriage or celibacy, let a man take which course he will. He will be sure to repent - Socrates

Love is not looking in each other's eyes, but looking together in the same direction - Antoine De Saint-Exupery