Not to be the bearer of bad news, and I’m not saying it’s for sure, but there’s a very good chance that she didn’t actually have a miscarriage, but she aborted the child on purpose to hurt you out of spite. And she just CLAIMED she miscarried. Sort of like Münchausen syndrome.. for attention.
And that’s a very scary thing if she aborted it and claimed she miscarried. If that is true, you might be better off without her in your life, because that’s not a good person to be married to. She wouldn’t be safe for future children. With that said, it’s quite possible the stress did make her miscarry, you never know
If you needed to talk to your ex about business, then you should have told your girlfriend about that ahead of time, BEFORE reaching out to your ex. You were wrong to hide that from her.