Maybe she's a nutjob. But she's PREGNANT. And scared. No support system. Facing the prospect of raising a baby alone. You have crazy hormones running through your veins that you've never had before, you probably feel like cr@p most of the time, your body is actually making another HUMAN BEING and 100% of your focus is being sure that that baby has the best possible future. I can imagine acting a little crazy under those circumstances and pushing for commitment. Also, parenthood is an enormous game changer. I can absolutely believe that she'd be willing to pivot 180 degrees if it was in the best interest of her child and stick to it.
Sorry, but I don't agree with the men on this one. Counseling and working on communication with a good therapist sounds like it should be a good thing no matter what, since you'll be in a co-parenting relationship at the very least for the next 18 years. Sure, see a L to be sure your rights are protected and know what the laws are regarding common law marriage in your state. Get your valuables out of the house and into a safe deposit box, if you're really worried. And, if you think she's potentially a physical threat to your safety, then obviously get out or get her out. But this is the mother of your child. Do you want him or her to grow up knowing that as soon as Daddy found out Mommy was pregnant, he kicked her out of the house?
Me (46) H (42) M:14 T:18, D9 & D11 4/19 - 12/19: series of escalating BDs 9/20 - present: R and piecing