What to do when friends betray?

I would simply stop adding any more currency to a friendship that is appearing to not be equitable in terms of what you invest. IMO emotions are best not squandered where they are not appreciated.

Does the peson know about your enmity with the other person? Sometimes one comes into a weird dynamic where one or the other of the two in the existing “relationship” are not honest with you. That makes it tough on the new party. Be sure you are up front about your feelings to the “friend”. If you have any value for the person, that is.
Sometimes it’s not worth it, and neither is the friend. You may want to weigh out whether the person’s friendship is genuine and worth your trouble. If you find that it is not, just erase him/her from your life and move on. Remain civil and courteous, but do not initiate any intimacies.
I find that erasing people is the best policy.

The way the question is written suggests that the despised person (your friend’s friend) is male. Is there a possibility that she has a crush on him? If that is the case, then she will always take his side, even when he’s clearly wrong. No one should ever support their friends unconditionally. When a person does something that is clearly wrong, or bad, or not nice, that person needs to be called out. Even if they are your friend.

Maybe have a nice little chat with your friend, remind her that there are good reasons (give a few examples) of why you don’t like this male friend of hers and ask her why she supports him when he is wrong or mean or whatever. Then tell her you have a hard time dealing with that and tell her that you feel slighted. If she sees the light, then you can probably remain friends with her. If she gets all defensive about this guy, then there’s nothing you can do. Just let the friendship die on the vine. Be civil, but don’t throw any energy into the relationship anymore.

It would seem that she has decided to think for herself, and has found your dislike of this person to be unfounded. It sounds rather controlling to expect a person not to like someone just because you don’t, without giving them a chance.

Perhaps you should see if this person has changed since they slighted you? If you’ve been in the workforce for 15+ years, you should be too old for dramatics. Do what you can to play nice in the sandbox.

Friendship is usually something where people give the same amount to something. Go with your gut. If you dislike your friend now, if it hurts to be around her you might as well or just distance yourself from this person for a while and think about what you want to do.

While I agree with @BarnacleBill that we cannot have expectations of people based on our own feelings, I do think that some friendships have a lifespan. Sometimes we just grow apart I suppose. If you truly feel that your friendship has come to its end, then perhaps you can create some distance between yourself and your friend.
If you really care for him/her and want to make it work, then it can. You can have a friendship on a different level – a level you’re more comfortable with.

NO!! DON’T DO THAT! the best thing to do would be to ignore that friend if you can for some time, if he is a true friend in the wrong and astray, maybe it will make him realise that and he may be your old freind again… to be honest I’m in a similiar dilemma myself and that’s what I’m doing. Just please don’t be nasty to the fellow.
hope everything turns out OK, GOOD LUCK .. . .

I suggest having a casual chat with your friend and explain that her friendship with the other person makes you uncomfortable. While you know she is free to be friends with anyone, you prefer to stay out of conversations about that person and their friendship. You can, and should IMO, ask her to respect your 15+ year friendship by not sharing personal information about you with the other person.

Basically, your friendship with her does not need to include the other person and their friendship does not need to include you.

I would just leave her twisting in the breeze a couple few times when she is wrong. It will feel good, and if she asks you about it you can diplomatically bring up your discomfort with the other situation. Remain friends with her and everything but just withdraw support when she is wrong.

Thanks for all the great reply’s. After review, I think I will just let this friendship slowly fade away. No animosity. I have given quite a lot to the friendship and she has given very little. Time to move on… Thanks again.

@Mutable I think you are choosing the best way. Good luck and try not to feel too badly about it. And hopefully the next new friend that you make will end up being really great!