She’s made all the mistakes, so you don’t have to… Ask Erin is a weekly advice column, in which Erin answers your burning questions about anything at all.

Q.

Erin,

I am in a horrible situation, and I don’t know WTF I’m going to do. 

My best friend of many years works with my brother-in-law. They work long hours together and have been out of town for a project. 

I started to get some suspicions that maybe something was going on between them, but then thought I was being paranoid or just imagining it. 

They returned from being on location for two weeks, and I had dinner with my friend. She was acting weird, and just things she said about the work trip didn’t make sense. So I had those red flags go up any time his name came up. 

I don’t even know what exactly prompted me, but I just asked her, “Did something happen between you and X (we can just call him X)?” 

She turned bright red, and she didn’t even have to say anything. Then I asked her what happened, and she told me that they slept together, not once, not twice, but three times. I felt sick because she is my ride-or-die, but that’s my sister she’s fucking over.

Now, what do I do? 

Do I tell my sister? Do I tell my brother-in-law I know? Do I end a 25-year friendship? 

I don’t know what to do. 

A.

Good grief, I do not envy your position. 

I’ve received many emails over the years from folks who find out a friend’s partner is cheating, and they wonder what they should do. Sometimes I tell people to stay out of it. Why? Because we aren’t always privy to the boundaries a couple has set up for themselves. And, unless we are very close to the person, we shouldn’t necessarily be the ones delivering the news. 

That said, in my first marriage, my suspicions about my ex-husband’s infidelity were confirmed by a friend, not someone I was particularly close to, and I was immensely grateful. It gave me the push I needed to end things. 

However, your situation is complicated because you are torn between your sister and your best friend. 

You can’t stay out of this one. 

So what should you do? 

You are under no obligation to give your brother-in-law a head’s up. Why? You risk him getting ahead of you here and poisoning her against you. I have seen this one too many times. 

Pick a time and space to sit your sister down and give her the information that has come to you. Just before you do so, let your best friend know that you will be speaking to your sister. 

As I pondered this, I thought about whether or not you need to divulge who the other woman is. I think you do. 

Why? Because she will want to know where the information came from, and I think there is no other way around it. 

What your sister does with this information is up to her. First, she may need to sit with it for a minute. Then, she may want to confront one or both of them. Finally, she may need to talk this through with you. 

Out of respect to your sister, don’t share this information with anyone else other than her, not even family members. 

She has a right to privacy as she works through the next steps. Whichever way she decides to do it is her business. It’s not your marriage; it’s hers. I mention this because it can be so hard to see those we love handle problems in their relationships differently than we would. We don’t want them to be hurt. But we have to let them figure things out according to what is best for them and their family. 

Whatever the fallout is, you are not responsible for this mess. 

You didn’t cause the infidelity. Instead, you allow your sister to know the truth and make decisions based on learning what’s up. 

As for your friendship, you don’t need to figure that out right this moment. Do I think you have to scrap a pal of 25 years? No. But I wouldn’t be inviting her to family functions anytime soon. I think you’ll need some time and space to sort out that friendship. You may be able to remain friends, but some of this will come down to how things play out with your sister. 

Good luck. I am so sorry you are in this world-class crap position. 

The information within Ask Erin should in no way be interpreted as medical advice because I’m not a medical professional. But I am here to help — to share the wisdom I’ve gained after years of making mistakes. If you have a question for me about relationships, addiction, dating, friendships, depression, parenting, sex, consent, what I’m watching, what I’m reading, what I’m listening to, Labradorite, or anything at all, use the contact form HERE or email me: askerin@erinkhar.com. As always, your anonymity is golden. 

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*Artwork: Tess Emily Rodriguez