My partner and I are poly and we're slightly experienced. He's got a new other partner. She seems nice and I'm fine with her and the whole arrangement so far. But the problem is she's insecure about my liking her. She's very flirtatious with me, and my boyfriend says she wants to sleep with me (we're both bi). But I think she just wants to because she thinks it'll make me like her.

She's pretty and all, but I don't know if I want to have sex with her. My boyfriend says he'd have a threesome if I wanted to but it's not a big deal to him. Or he's okay with my sleeping with her alone.

So I guess I could if it would make her feel like I accepted her. What's the etiquette here? Is this a common "welcome to the neighborhood" kind of thing in polyamory?

Do not fuck this woman.

Now that we've got that established, this is something I see happening sometimes in polyamory, especially in the situation you mention: two bi women dating one man. Your letter struck a particular note with me, because I've been there myself. I've been the new girl, using sex to (in my mind) smooth my relationship with the alpha female while I had a relationship with her partner. And more recently, I have also been the incumbent partner, having the new partner be seductive with me in a way that felt like she had motivations other than pure lust.

Assuming you're correct about her motivations, her doing this doesn't make her an evil woman per se, although I think it means she's a bit immature and possibly manipulative. But regardless of what's in her head, the best reason to fuck someone is because you're sincerely hot for them, and you don't sound sincerely hot for this girl. So you should not fuck her. You are not being unwelcoming, and there is no polyamory rule that says you have to assuage the new partner's insecurity by eating her pussy.

For all the people who are thinking, "What, a good-looking woman wants to fuck and you're saying no?" my response is, "Think beyond the orgasm." This is not a zipless fuck; this is your partner's other partner. What if you give her what you think is a one-time welcome fuck and she falls for you? Or on the flip side, what if you have sex and it's terrible and she never wants to face you again? Both those scenarios are awkward in themselves, and they would play havoc with your boyfriend's relationship with her. That would create some tension between you and him, which you don't want.

There's an unflattering phrase for sexing someone just to make them feel better: pity fuck. I can't believe that's what this girl wants to be. She doesn't need sexual charity—she's dating your sweetheart, right? So she's clearly doing pretty well in the world of love. Express to her kindly but clearly that you wish to keep your relationship platonic, and let her get over her new-partner nerves somewhere besides between your legs.