I am married over 30 years. Before I met my husband, I was engaged to some one else. We even had tenoyim. Many people didn’t want to go out with me because of this. Smart Cookie, it STILL isn’t a reason to go through with the marrige rather than breaking an engagement.
Some one looking to go out with a person who was engaged once should ask if there was tenoyim because then you do need a shtar mechila. Otherwise you don’t. Understand that when you ask what went wrong, there are 3 stories: his, hers and the truth. Each party will have the story as seen through their eyes. Even if they broke of because one side was obnoxious and abusive, do you think that person will see it that way? I don’t think so.
As with anything, you are entitle to ask questions as long as you don’t embarass or humiliate the person. After 30+ years, I still feel badly about a certain person who did his best to “pick me apart”. Have rachmanus.
Hatzlacha raba.