My brother's SO randomly expressed to me that she's never been comfortable with the friendship. My brother backed her up, saying that it's insensitive of me knowing how she feels about it.... Like what? You've never had an issue with me being friends with your ex before?

First of all, his ex and I have been friends for years. They broke up like 15 years ago. She's also happily married to a great guy, who my SO is friends with as well.

Am I wrong for this? I mean I feel bad that she feels this way.