Heard gossip about a friend and I feel guilty keeping it a secret

r/

About 3 months ago my friend Kim (30F) made some horrible comments about our other friend Caitlin (29F), and I feel guilty about keeping it a secret.

I (26F) turned to Kim for advice after Caitlin hurt my feelings, expecting comfort and guidance I instead was met with several cruel comments about how Caitlin is unemotional and that this negatively affects her ability to be a good friend, a good employee (for reference we all work together), and one day a good mother. I shut down some of these comments in the moment but I was so shocked I sort of sat there stunned and in silence.

I’ll be honest it isn’t the first time I have heard Kim make bad comments about others, in the 2 years we have all been friends she has shown a bit of a pattern of speaking negatively about friends and colleagues – but Caitlin isn’t aware of this. I have actually been trying to distance myself from her more because of this. But I didn’t expect this level of brutal honestly about Caitlin at all, especially as she knows that Caitlin and I are incredibly close.

After this happened, I sought some advice from other unrelated and unbiased people in my life who all told me the social convention dictates I shouldn’t tell Caitlin. I didn’t like this as my gut told me I should share it, but I also was so scared of hurting her that I listened. It has been several months since this happened and I still think about it regularly. Caitlin has been hurt in an incredibly similar way by a friend in a previous workplace who also gossiped about her behind her back. I am fearful that by not sharing this I am potentially going to end up letting her get hurt in the exact same way. But at the same time I worry that if I do tell her that I might blow up her friendship in a way she doesn’t want to happen. Every time I see them interact at work my blood boils, I am so angry at Kim for putting me in this position, and so sad that Caitlin has no idea.

I don’t know what the right thing is to do, but I hate that I am forced to live with this secret alone. I cannot decide if sharing is going to be more hurtful or helpful in the long run. What would you do in my situation? Has anyone been in this situation before and what happened?

TL;DR: My friend and colleague Kim made some horrible comments about our mutual friend Caitlin and I feel guilty about keeping it a secret.