Apologies in advance for the slightly inflammatory title, but headlines rule the media. Specifically I'm looking for some ethical consulting from people who actually practice ENM.

I (29m) am seeing someone (32f). We've only started seeing each other again recently, however we used to date, and have been good friends for about 8 years. In my opinion, her nesting partner / primary (30-something m) is kind of problematic to their relationship. I met him a couple times years ago when she and I were just friends, and never particularly enjoyed his company, though had no reason to dislike him.

They've always been non-monogamous, however in the last couple years he's decided he "Hates poly" and has asked for a DADT policy where he doesn't ever, ever speak to, see, hear or know about anyone else she's actively seeing, used to see, or is even just potentially interested in. Currently he's just monogamous with her, she is actively seeing other people. She's expressed a good deal of frustration to me (prior to, and since she and I sparked things up again) about how she's respecting his wishes, but it's both uncomfortable for her because it makes her feel like she's sneaking around behind his back, and also because she feels like she has to hide a big portion of her real self from him. (They're in couples therapy, I am not trying to fill those shoes.)

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Now I'm in a bit of an ethical conundrum. Knowing all this, and some additional nuances, as her friend what I want to say is "Girl, dump his ass. You can do better. You deserve better." She can be slow to set boundaries because she gets worried about hurting other people's feelings, even if not establishing a boundary is actively hurting her. And I want to be supportive, and encourage her to advocate for herself (in whatever way that manifests.) However, we're sleeping together, and there's romantic interest we're still figuring out the details of. At which point, to me it feels fairly unethical to (while I'm actively vying for more of her time and attention) to say "Oh yeah, leave him" because the unspoken part of that is "and come spend time with me." and that just feels icky. Advice?