Wow. He fairly recently revealed to you that he's been deceiving you for years and opening you up to risk you didn't know about (everyone should have the right to choose if they're comfortable with sleeping with someone who has other partners, safety-wise), and he expects you to be "concretely working" towards the "goal" of a threesome and to be chill about him sexing up any random lady he meets on the road. I'm sorry, but he sounds from this angle like an entitled ass.
You have every right in the world to take this at your own pace and 6 months is NOT a long time in the course of a 10 year relationship, especially when I imagine that your time and energy are a little eaten up by your two young kids!! Geez.
Poly does *not* mean you get whatever you want whenever you want it, and it really sounds like that's what he thinks he deserves. To my mind, it's supposed to be about love grounded in the context of balance, negotiation, compassion, honesty, and empathy. He has a lot to make up for in terms of his lies to you, and is in no position to be making demands.
Don't let yourself be rushed or pressured into anything. You don't have to do anything you don't want to do. His choices are his own, but you have the right to be clear about what you're ok with and what you're not, and it's ok to not be ok with some things. I imagine banging random chicks is a want for him not a need, whereas you may *need* to feel safe right now which that may not be conducive to.
You've done a tremendous amount of growing and learning over the last 6 months, from the sound of it. Does he appreciate that?
Is he open to the idea that you might choose to be with another man, if you decide to embrace poly for yourself?
Is he open to the idea that it's enough -- more than enough -- for you to open yourself up to the idea of him wanting to be with other women and that you are not required to participate if you decide poly is *not* for you?
Though, really, I'm not sure where the poly"amory" part comes in here... is loving emotion a factor whatsoever in his desire to be with other women?
The major players. Me, 30ish bi female. Gia, girlfriend of 4+ years. Clay, boyfriend/dom. Davis, ex/friend/"it's complicated." Eddie, roommate & fwb.
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy and Nikki, Clay's partners. Liam, Eddie's husband.