My best friend lives in another city but visits about every 2 months. Last time they were visiting they got close with my ex [23M] who treated me really badly during our 3.5 year relationship, has a history of drug and alcohol addiction and sexual misconduct (I say misconduct here because no one has ever said "abuse" but basically he really should have been getting clearer consent...ya know...) I didn't know about them getting close until they kissed and she told me about it the next day, coming to my house crying.

I was upset and asked her for some space for a while as I worked out my feelings regarding the situation. She want back to her city and unbeknownst to me, kept in contact with the ex and they fell in love yada yada.

Cut to a couple of weeks ago, she asks to meet me as she is back in my city. I accept and see her where she informs me they are dating. I was caught off guard as I hadn't expected that at all, and play it off as no big deal.

Later I become very upset and angry and betrayed that I was never involved in this process. Me and my best friend were extremely close (or so I thought...) and would call each other soul mates and I've never been the kind of person who understands valuing romantic relationships over friendship - I value relationships based on the level of closeness, intimacy and trust, which I believed we had a lot of.

My friend apologized, saying they knew they hadn't treated me kindly but they also didn't regret their relationship with ex as they had learnt a lot already and felt really positive about it. She also said that the reason she didn't tell me before we met up was mainly because she was scared. I said I was happy for her even though I don't like him but she really should have told me. It really fucking sucks to find out your best friend is dating your ex AND you're the last person to find out.

She kind of ruined her initial apology by saying she thought she was doing the right thing as I had asked for space.

I have a lot of trust issues and I especially hate being lied to and having information kept from me. The ex she is seeing is the one that cheated on me more times than I can count, keeping things from me and lying right to my face over and over.

Right not I feel like this relationship is beyond repair. It's over. I am absolutely gutted. She fucked up and I don't think I can forgive her.

But here's the trickier part. I'm now feeling a strange dislike of everyone around me, especially my current partner. It feels like he's doing everything wrong. From not being there for me in the right ways to playing too many video games.

I struggle with depression and anxiety and possible other un-diagnosed mental health issues which is making me wonder whether these are real feelings or not or whether the situation with the friend has triggered an increase in social anxiety and depression feelings which may be manifesting as anger and mistrust? But I'm also thinking of all these signs I'm seeing of why he's not a good partner might be real - I don't know. I'm feeling super crazy and I'm also taking a lower dose of my SSRI medication (under my doctor's supervision.)

But what if it is real and I'm just in denial? I feel trapped and I don't know who to talk to. I would usually talk to my best friend about these things. I have a therapist but I won't see her for another week.

tl;dr: I had a falling out with a best friend because they kept the fact that they were seeing my ex from me and now my partner seems to be doing everything wrong but I don't know if it's because of my mental health or if it's real. I'm hecka scared :( and I don't know what to do.