Hmm, this so called poly life has gotten off to a really rocky start!
First of all, you have young children and another on the way. Practicing poly with kids in the mix is extremely complicated. Kids take a lot of time, at all ages. I sure hope you're not allowing your h to date his gf while you stay at home doing childcare. Do you and your h go on dates yourself, or does he get to go out with his gf, and you and he never have quality time kid-free?
Second, the cheating. I'd feel so sick with betrayal, knowing h and the gf fucked you together while they were both secretly fucking each other! And now that their relationship is in the open, she won't fuck you, or even hang out as a friend with you! Yuck!
How do you "limit" what your h and his gf do on their "dates?" Are you not allowing them to fuck anymore? Are you sure they aren't? He's already been capable of deception once, and so has she.
You say your communication is so great. Then, how do you explain the disgusting cheating? How do you trust him now? What the HELL was he thinking?
Now, as to the idea you want to be good friends, confidants, with your metamour(s): this may or may not happen. When your h dates, or you do, eventually, you get to choose someone YOU like. As long as his partner, or your partner, can act civil, there is no need for this partner to be good friends with their partner's partner (metamour). That is too much to ask. It can happen, and it's nice (my gf and my bf get along great, but he's the first bf of mine she's been so close with), but don't count on it.
Maybe, once you have time, YOU can find a gf who will be your lover and confidant, love your kids, help you care for them (and vice versa, if she has some kids too), hang out, drink tea, go shopping, take the kids on adventures, watch a movie at night, etc. Don't count on your dh to provide that woman for you. Go get one.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
me: Mags, 59, living with:
miss pixi, 37