My DP's ex stops contact for the silliest of reasons with alarming regularity. The difference is we have a court order, so can and have gone back to court for an enforcement order. I understand why he feels it's best not to rock the boat, but honestly, it just doesn't work like that. It doesn't keep things progressing, or civil, all it does is show the ex that she can do or say whatever she wants.
Honestly, it's stressful even with a court order, but DP knows that when she's being massively unreasonable, he has a path to take, rather than just hoping it all blows over.
We're also TTC, and we discussed how his ex would react if we do conceive. Again, if she was to react badly, he'll be going back to court for an enforcement order.
DP's ex also had a problem with me meeting their DC, and tells them that they don't have to listen to me, talk to me or do what I say. Every time they're here, we have to point out that I'm an adult, it's my house and that our house has rules. It's irritating, but they quickly forget her rules, and just fit in ifyswim. The court knows that she does this, and she has been told by cafcass that she needs to stop. If she continues with this, and her other behaviour, they've said that they'll be recommending a switch in who has residency.
But the only reason why we have these options, and back up is because DP went to court to have his access set in stone.
You're two and a half years down the line. She's unlikely to turn around and suddenly start being reasonable. He needs to go to court.
As for your pregnancy, first of all congratulations. As I said, we're TTC, so we decided that if we get pregnant, his ex would get a short text at the six month mark simply saying that we're expecting, due date X month, and will be preparing the DC for new arrival. After we had told the DC ourselves.