Asking a formerly solo person to be fidelitous with an established couple (also known as unicorn hunting), especially right off the bat is somewhat problematic to me. The established couple, especially if they're long-established, are going to have a deeper and a different sort of partnership than the new, third person. The established couple gets the stability of their set habits and comfort together, plus the excitement and uncertainty of new love. The new person only gets the latter and it will generally be a long time, if ever, before they are really integrated into the couple's partnership and are a full member and an equal in reality, not just in intention.
I mean, after all, isn't the whole idea of poly that you can have commitment without exclusivity?
Of course, that doesn't make the fact that your ex was lying to you ok... I just think it's worth considering that your expectations of new partners might be a little unreasonable.
As for your present situation, it's not fair to expect your bf to disrupt his relationship with his daughters for you guys. *However*, if he was ok with them getting to know you and with being out to them, you could see him much more often without forcing him to take time away from them. So, I see the fact that he's keeping them in the dark as the biggest problem here.
It's not fair to consider moving his girls in with you guys while they are still unaware of the nature of your relationship. As teenagers they're old enough to understand these things and certainly old enough to feel very betrayed if they're lied to.
If he's serious about this relationship, he needs to come clean to them, so that you all can spend more time together now and so that you can have a future together. Waiting a while was perfectly reasonable, but a year is long enough. After all he'll have to tell them if/when he has your child, right? If they're going to have to know eventually, why not save a lot of the angst and do it sooner rather than later? He doesn't have to tell them that it's been a whole year, I think it's okay to fudge a little on that part.
The major players. Me, under-30 bi female. Gia, girlfriend of 3+ years. Clay, new boyfriend/dom. Davis, ex/"it's complicated."
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy, Clay's partner.