I'm afraid my friend's relationship has become toxic and I don't know what to do

One of my closest friends (18F) has been in a relationship for about 8 months, and I (18F) am really struggling with how to navigate it without overstepping.

At the beginning, I got along okay her boyfriend. I at least had no strong negative feelings toward him. I just thought the important thing was that they made each other happy and everything was healthy between them. But over the past couple of months, I’ve started noticing small but consistent behaviours that have changed how I see him. There have been moments where he comes across as very arrogant or “too big for his boots,” like he sees himself as above other people. He’ll make comments about people he considers “less cool,” and those moments have made me very uncomfortable and honestly icked out.

I initially brushed it off, but things escalated on a recent night out for my friend’s birthday. He was quite drunk and began mocking a stranger on the bus, seemingly to impress us. It felt very mean spirited and unnecessary. So later that night, while we were waiting in line for a club, his behaviour shifted dramatically. He became visibly very angry and started yelling and blaming my friend for the situation, saying she had “dragged him out” and accusing her of wanting to act single and trying to get attention from other guys. It felt completely ridiculous, untrue and unfair. At one point, he pushed her away with honestly quite a bit of force and stormed off, and she ran after him.

I then spoke up and told him I didn’t agree with how he was treating her, and in response he told her to “get me to shut the f up' or he would “crash out” at me. That moment honestly scared me, which was a turning point. Up until then, I had been telling myself that no relationship is perfect but seeing that level of anger made me question whether this dynamic is actually healthy at all.

Since then (a week ago) I was together with a mutual friend, and she told me about a recent argument they had which she had not told me (we are very close friends) In which what she told me and then other things I observed

-He has yelled at our mutual friend on that night for an extended period and made her cry

-My friend has been so distressed after that argument that she has been physically unwell

- He can become aggressive and has pushed her before

- She often feels she has to apologise first

-There are financial dynamics where she pays for a lot, including things like drinks and expensive tickets

When I decided i needed to speak up and expressed concern to her over a message (which i debated for a while), she wasn't unkind but told me I don’t “see the whole situation” and that their relationship is fine. She also seemed more upset that others might view her relationship negatively than about the behaviours themselves.

This is where I feel really conflicted.

On one hand, I care about her deeply and don’t want to abandon her or push her away. I’m very aware that I don’t want to come across as controlling or as if I’m trying to interfere in her relationship at all. I also know she is very protective of it, and I know that anything I say will likely be shared with him, which makes me anxious about it turning into a “me vs him” situation.

On the other hand, I’ve reached a point where I feel genuinely uncomfortable being around him. His behaviour, especially when he drinks, makes me feel uneasy, and at times even unsafe. I also feel like I can no longer support the relationship in good conscience. Another layer to this is that they are almost always together, so it’s very hard to maintain a friendship with her that doesn’t involve him. It feels like she has become very intertwined with him, and I’m starting to feel a sense of distance from her because of it, which I hate. I feel guilty even admitting this, but part of me has started to feel a kind of emotional withdrawal from her because I struggle to reconcile the person I know with the situation she is in. I know this is unfair and in toxic relationships I must be there to support my friend but she doesn't think she is in a toxic relationship and I don't want to be that person that is creating a 'drama' out of 'nothing' and I'm just very conflicted because I also don't want to involve myself so much to be placed in the role of their 'relationship mediator' which I have done before after being dragged in with their smaller conflicts and it was exhausting. I don't blame her for not seeing the bigger picture and for loving him but it's still difficult and i don't know where that balance is. Where is the line between expressing concern and overstepping? Is this that concerning that I should be involving people like her parents? Because I fear it could become bigger and worse and I think she has been hiding more intense things from me and I think the toxicity might run deeper than I can see from the surface. For example, until that night I didn't know that she was paying for 80 percent of his things, or how aggressive he could be towards her. Is it reasonable to set a boundary where I don't want to be around him? How do I maintain the friendship without either compromising my own values of pushing her further into defensiveness? And realistically, is this kind of behaviour something people see as 'normal' at this age or is my reaction justified?

I would really appreciate any perspective on how to handle this in a way that is supportive but also avoids conflict and respects both of our boundaries

To confess I honestly just want things to go back to before her relationship with him no matter how selfish that sounds