The couple I wanted to invite, I'd known for years and my wife (to be) knew the woman of the couple fairly well. We'd worked at the same place and, after I left that job, both my wife (to be) and I visited the couple regularly. 

(Of course, they are fictitious and, for the sake of privacy, I'll refer to them as Roger and Natalie)

You'd be hard pressed to find a nicer couple and I saw no signs of there being any problem between the two women on any of the numerous visits we made to their house for tea. We attended their wedding.

By the time we married, Roger and Natalie had had three children. It was 'a given' that they'd be at our wedding, or so I thought.

Despite the fact I come from a small family and had very few people coming to the wedding, fictitious wife-to-be informed me that she didn't want Natalie to come.

This was an early red flag and, in retrospect, I should have cancelled the wedding. Maybe I would have done if we didn't have a fictitious child on the way.

Secondly, I should have talked to Natalie who, twelve years later told me something that would have been another red flag. It was obvious that Natalie could see right through the woman I was marrying and a conversation with her could have saved me years and thousands of pounds in money.