Trusting, Yes, your xh is caught between a rock and a hard place. She may be pushing the marriage, but time will tell if your xh will step up to the plate. This woman just might push so hard, that the entire situation may go the other way....out the door! She is really trying to pin your xh down and you are right...she is very insecure because she is very much aware of the time that he has been spending w/you. OP get very territorial when this happens.
I'm so sorry that your child had to hear that conversation. I still think it was intentional and what adult would do such a thing in front of child is quite mind boggling and very selfish and immature. I'm sure your your child was upset by the conversation, and quite frankly, who wouldn't be?
I do hope that things will settle down and there are no more conversations such as this in front your child.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.