It sounds to me she has been spoiled a bit on the nature of your union. It can come from the ex, and her own observations. It could have been a dig on you because her husband to be is your ex.

No one knows the true face of someone else's relationship. The outside appearance is often deceptive. For example, the people I know see me and my wife as one unit as opposed to individuals. They don't know the problems we have faced and are facing. The assumption is that because we have been together so long, we are perfectly happy. If we split up in the future, which is more probable than not, will be a " didn't see that coming" moment for those that know us.

My guess is the fiance in this scenario sent out some negative emotions to you for 1) being an ex, 2) judging what she has heard about your relationship from your ex. 3) solidifying her position as the SO with your ex. In other words, its her insecurity.

Seahound