So, Reddit, here's a doozy for you. I'll try to leave out as much detail as possible just in case anyone from the story finds this post.

I (32f) have two cousins (18f and 26f) who have the same mother, but a different father. Long story short, my aunt had my cousin A when I was 4 with her husband at the time. They got a divorce, and my aunt remarried and had my cousin B at the age of 40. I was 14 and A was 9 when B was born. B's father, like my aunt, had a son C from a previous marriage, who was about A's age.

When my aunt remarried, her husband came from another continent all the way here to live with her and their newborn, and his son visited quite frequently. However when they got a divorce a few years later, the husband moved back to his continent.

Rather recently, my aunt and cousins decided to pay B's father a visit all the way in his country. They had a good time, however, A developped feelings for her sister's brother. I have no issue with people being attracted to one another, however A started using her sister B as an excuse to speak to C. She'd say things like "We should have a video call all three of us!" And they would, but A and C would ignore B while talking all hot and heavy on the video call.

My cousin B and I are rather close. She always considered me a trustworthy person, and she confides in me a lot when things go sour between her and my aunt, or for her general anxieties. So, naturally, feeling uncomfortable that her brother and her sister were developping an intimate relationship, she came to me about it. I was outraged. Not only were they putting her in a situation where she'd have to explain "my brother is dating my sister", but they using her to get to one another. And that was absolutely unacceptable to me.

So, here's where I might be the asshole. Cousin A never came to me to talk about it. But I lost my cool and called her up to asked her what was up with that. I asked her how she could be using her sister as an excuse to talk to C and how she could be feeling good about it when B had clearly expressed her discomfort about the situation. I said it was unacceptable that she'd treat her little sister that way and put her in such an awkward position. And that if she didn't stop it, I would be too uncomfortable with her priorities to keep in touch, at least until she genuinely apologized to her sister. A answered remorsefully, said she felt bad about it, but that she couldn't help her feelings, nor could she control C's. So I said to her that that was the stupidest excuse I'd ever heard, because, sure she had no control over her feelings, but she did have control over her actions.

A decided to go through with it anyway. It didn't last very long, but she still went through with it. The brother visited, never even got in touch with his actual sister. So I cut my cousin off. I haven't spoken to her since, even if she's expressed shame at the relationship. B told me A had never apologized.

My aunt says I'm over reacting, that A is in shambles over it. That she feels so ashamed. That I should reconsider because B has reconsidered and has "forgiven" A (although she still tells me how angry and uncomfortable this all made her feel, and about the fact that C hasn't even tried to get in touch with B at all despite being her sibling and dating her sister).

But I don't want to get back in touch with A until she genuinely apologizes to B. And now, my aunt won't speak to me either (which is kinda fine with me anyway). I've refused A's calls and listened to her tearful voicemails without returning the curtesy. My mom is on my side, but since A and B's mother, my aunt, is a terrible maternal figure (story for another time), she feels bad leaving A without any support at all and still talks to her.

So, reddit, what do you think? Am I the asshole here? Should I get back in touch with my cousin and hear her out? Or am I justified?