I definitely think that you should try more of a triad, since everything else seems to be progressing okay & everything is being honest & open. I'm not saying all of you go jump in the bed together of course.....take your time, date all together, try some dates just you & her (hold hands, snuggle on the couch, etc). Of course you'll want to talk to your husband & her about it and all of you be in the same page....that's very important.
And if he's telling you that you are his world then believe in that & don't allow the affection/attention he shows for her to make you feel that he loves you any less. Like I said it's all new & exciting right now.
As I said in the previous post I definitely think there are feelings developing & it's progressing past friends w/ benefits. Especially if she's there as much as you say she is & they talk as often as they do....she's becoming a part of your family which can be a wonderful thing for everyone....there's more love, more support, more affection/attention.
And no he definitely shouldn't push you away & if you're feeling pushed away then you have to be open & honest with him about it. When you talk to him about it don't attack him (that will immediately cause an argument & you'll get no where), tell him this is how you're feeling or when he does this or that it makes you feel this way. Try to find a way to resolve those feelings but figuring out what you BOTH can do to make it better.
My husband & I from day one have always been of the mind set that we're stronger together & we get through everything together, we're in this life & marriage together and we work through all the ups & down as a team. And that has gotten through a lot & we've only gotten stronger because of it.