<human>: Could you distill the essence of the text into 1-3 sentences?

I have a slight dilemma. I am currently staying with 4 other people away on a placement.

Now, out of the total 5 of us, it has formed into a trio and a duo. I'm with the duo. That is fine with me. We have a great time together. Until I spend time with the duo. I do not know what it is, but those 3 cant seem to gain her trust somehow.

I've known her casually for 4 years at university, but she has taken a real liking to me recently. Which I'm fine with.

So I was invited to have mexican with them whilst she was out having dinner somewhere else, and we all knew she wouldn't be back til late.

We had a good time, enjoyed eachothers company.

As soon as she came back, we both went into our shared bedroom and she automatically felt very cold towards me. Almost pissed that I had spent my night with them, not her.

I like spending time with them. I'm not going to stop that.

So we talk about out days and nights etc, and it eventually turns to a conversation about the trio.

She has nothing but bad thoughts and comments about them, and I can't stand it. Everytime she talks badly about them, I feel like I have to counter balance it in a way that is calm and does not offend either them or her. But even though sometimes I'm right with my facts, she seems to be pissed, almost thinking that I'm on their side, even though I specifically told her that I wasn't.

If someone could help me understand why it's like this, and what I should do to calm down the tension between her and the trio?
<bot>: Living with 4 other people, One close friend speaks ill of the other 3. I don't want to be a part of it.