I know that I've gotten upset in the past when things about me have been shared that have nothing to do with my husband and his girlfriend. Even if she is going through something similar, my stuff is mine to share, not his. I've asked him that he clear it with me or ask her to talk to me directly if it is my stuff that I own. In the same spirit I don't want him sharing things with me that she has told him in confidence about her that have nothing to do with me. Although if it's something that does affect me then I have said that I need to know those things (ie when "I love you" happens or discussions about changing living arrangements, even if they are just what if conversations).
Everything will be ok in the end. If it's not ok it's not the end.