How can I support my friend in maintaining halal boundaries?

Assalamu alaykum. My closest friend, who reverted to Islam some years ago and is quite knowledgeable, is currently in a situation that concerns me. She's met a good Muslim brother, but their interactions have been crossing into haram territory-starting with private messages, then calls, and now meeting alone together. It feels like it's gradually worsening. I worry that he might be taking advantage of the fact that she's a revert without Muslim family support. I've talked to her many times, suggesting things like keeping communication in a group to avoid one-on-one contact, but it doesn't seem to make a lasting difference. In our country, mosques aren't very responsive to such issues or marriage guidance in general. I genuinely want to help her without being pushy. Perhaps she's hesitant to set clear limits because she's found someone after a long search and fears losing him, or maybe she's unsure how to enforce boundaries. As for him, I don't know his intentions. Does anyone have advice or perhaps Quranic verses that gently highlight the consequences of haram relationships? I'm looking for a compassionate approach to guide her back to what's halal.