I am hoping that it is just a 'new to poly and freaking out' situation, as such I'm willing to accommodate that.
It's not just a 'new to poly and freaking out' situation. Sure, it's being spun that way, because then...you'll accommodate it. And so will he. Because we need to accommodate our poor little pwecious and her Deep Important Feelings that simply MUST be more important than anybody elses.
BULLSHIT!
Being new to something doesn't mean that everybody else's feelings get put on hold for that person. Being inexperienced does NOT mean that the inexperienced person gets to call all the shots.
Jesus Christ, imagine that happening anywhere else: We have a new pilot. New pilot is feeling insecure about his/her abilities and skills flying. So we're going to let him/her just keep trying until they feel comfortable...and if we all crash and burn along the way, well, at least we didn't hurt the new pilot's feelings.
Does that sound insane? It IS insane. And ridiculous.
New Poly Chick and certainly decide how quickly SHE is going to descend into poly. She can decide she got in too deep, too fast, and renegotiate her relationship with you, and with the other partner. She can *ask* (ASK, not demand) if the two of you might accommodate some reasonable requests (which I'm not going to go into now, other than to say nothing she's demanding is reasonable) in the relationship dynamics between the three of you, temporarily, while she has some time and space to sort herself out. WHICH, she should be TELLING YOU "If you do X for me to give me time and space, then I will do Y (get therapy/read self-help books/have talks every other day with you and Other Partner) to improve my comfort level and ability to handle this.
What she doesn't get to do is dictate all your relationships. Especially since the two of you have a child and have known each other much longer! That is NOT ok! In any way, shape or form.
If I were you, I'd cut all ties with her, let him know what kind of relationship you're willing to have with him, and then focus on you and the baby. And the other people in your life who aren't willing to kotow to controlling manipulative requests that come in the guise of "needing help".