Important person going away


New Here

Hoping someone can give me some perspective, advice, or something else on this topic. For background, I have been recommended by my therapist to pursue a PTSD diagnosis (lots of employability reasons for me not to which is why I haven't) related to waking up next to a dear friend dying following a suicide attempt. That honestly makes it sound worse than it is but I've reworded it 5 times and that feels the best way to put it. I've only really been experiencing the more emotional dysregulation side of PTSD for about a year I think but COVID's made it hard to isolate things from social disruption and cabin fever. So if I'm not a True Scotsman, let me know.

Apologies if this thread has ended up being more about my personal life and wayyyy less about PTSD. If this is too off-topic, mods feel free to remove it.

We'd had a close relationship for about 4 years, and that's going away right now. We'd been on the rocks for most of 2020, on-again off-again (mostly at their discretion). I noticed when we weren't really talking, or I felt they didn't want to talk to me that my PTSD symptoms got a lot worse. I had more emotional dysfunction, would have more frequent flashbacks, and especially more prominent nightmares. It felt harder also to not feel with overwhelming certainty that she was dead, as in harder to break myself out of those moments.
Well, we'd just recently (~ a month ago) started talking and seeing each other again. I was very excited for this, because not only does it mean that I would feel more stable as baseline, but also they're a dear friend and I enjoy their company very much.
They suffer from some pretty debilitating depression. Which is on my mind somewhere in the background pretty much all of the time. Well, a psychiatrist friend of mine and I started talking about some stuff relating to my PTSD, and I thought to myself "huh, I wonder what they'd say about a hypothetical person that experiences the symptoms that my dear friend does". We got to talking about it, me listing the symptoms that I know of, and my psych friend said to me "you know, this actually sounds like it could be fit a BPD profile". That didn't make sense to me given what I knew about people with BPD, but my psych friend said that a lot of this stuff was cutting edge, and that BPD classification was getting wider and wider. Well, I thought to myself, if my dear friend has been misdiagnosed this whole time, maybe letting them know about this new information would help them in seeking more useful treatment.
So, I did. I told them that they should talk to their therapist about it, and they said they would. Then they texted me a few hours later showing some well-researched articles about BPD that was more in line with what I thought I'd known about BPD and some experiences they'd had with family members and friends with BPD, and asked if that still sounded like them. I said no, and that being inside for this long has made me question a lot of things and they probably shouldn't take anything I'd said seriously and apologized. They reacted fine. Great!
And then I woke up the next day to a long text saying that what I'd said about BPD made them fundamentally question themselves and their relationships, that I'd made them think they actually had BPD for a little bit there, and that they felt for some time like maybe everyone had been lying to them for their whole life. Then, they asked if I thought we were good for each other to be around.
I did not react well. Honestly, it was paragraphs and paragraphs that I do not remember well. I even had a therapy session during that time and MAN do I hope that was okay. I came back into reality a few hours later, read our texts, and wanted to vomit.
I'd said that we weren't good for each other, and that we hurt each other a lot. They'd basically requested that we not be close anymore, that we take some significant time apart. They agreed to calling me on the anniversary of their suicide (a time that is particularly hard for me) to help reaffirm that they're okay then. I couldn't back off my words or explain what had happened without being so much more confusing, so I agreed.
Spent about a week thinking that I might be abusive since I'd made them feel gaslit. Called some exes, asked my friends if I had tendencies like that, they all said no. But they've not seen me in a while, and knew me before I got PTSD-y.

As far as things that relate to PTSD go: This is the most closed off that I've been from my friend, ever, since meeting them. I worry constantly, but other attempts to reach out have fallen flat and I don't think the next time they'll be even that receptive. I'm aware fully that any more involvement in their life at this time would be disrespecting a boundary, but frankly I don't know how long it's gonna be when I start losing control of what I'm doing again, and I'm very afraid that I'm gonna try to reach her when I'm like that. At the same time, I'm becoming more and more unsure of whether I was a good person to them this whole time. And even if I hadn't been hurting them like that since the beginning, has the emotional dysregulation made me into a toxic person? Cherry on top, I worry that I'm going to get worse and worse with them all but cutting off communication with me. I'm really feeling lost on how much control of my life I'm gonna have, and I'm a year away from finishing my degree. No more safe-zone of school, it's gonna be full-on primary-career-job time and I can't f*ck that up this early in the game.

Any advice, peace of mind, or guidance would be greatly appreciated. It's been a very dark week so far.