Need an Opinion from Others //abuse? warning//

Hello, I have been in a relationship for 2 years with my highschool best friend who I’ll refer to as R, and felt I needed an outside non-bias opinion on my situation.
At the start of the relationship it was revealed that at thirteen years of age, R was diagnosed with bipolar disorder and anxiety. A few months later into our relationship I went through a deep depression and was soon diagnosed with depression and anxiety.
Things have always been up and down in our relationship, it was soon realized that R had an eating disorder as well as body dysmorphic and we fought almost each day as we both are very emotionally unstable.
R comes from an abusive family, that even now is still abusive, however that’s not the point here.
R always had a habit of lashing out at me everytime she is mad, stressed, feeling bad about herself and this only has become worse overtime.
In her episodes of body dysmorphic she’ll scream at me, calling me a liar.
About a week ago it got worse, we were on our way to a party and had to catch the train, then we would have to catch a bus – we were both incredibly anxious, especially me as R had a habit of speaking to me like I am stupid when I’m not sure of something (but doesn’t seem to realize it).
That’s when R asked me what time the bus came, I didn’t know so I panicked and couldn’t speak. That’s when R started getting incredibly mad and impatient, saying ‘tell me or else I’m going home,’ ‘I’m not ****ing waiting for the bus,’ ‘why won’t you tell me?’
I tried to reassure R by saying it’ll be okay and we didn’t need to worry but R got more impatient and angry. “Tell me!” R yelled and grabbed me by the shoulders and shook me.
I yelled back not to speak to me like that and that’s when R stared at me in hatred before storming off.
That’s when the train pulled up and I yelled “bye” out to R, I went on the train and sat down, only to watch R race/storm after me, grabbing me and shouting:
“What the **** is wrong with you?!” and “You’re disgusting” over and over again. I told R not to touch me and how dare R call me that. I was devastated because this wasn’t the empathetic, gentle person I knew.
After this we got off the train where R demanded to have my phone to call their mother, so we could leave. I didn’t want to and I told R no and that everything would be fine.
R was even more hysterical, screaming and yelling at me and shaking me. I was terrified out of my mind. I asked why R was acting this way, calling me such cruel things and treating me so horribly.
“Because you didn’t tell me the time!” R screamed with rage.
I asked if R thought it was right to do this and R said I asked for it because I was basically screaming that I was being abused, that’s when I said that R was becoming like their abusive father.
R slapped me across the face with the coldest, most heartless look ever. It was heartbreaking and I started crying, and called R’s mum desperately to take us home. R’s mother told me to keep calm and stay there and R stormed over and I screamed for her R to leave me alone. R screamed in my face saying “You should have ****ing told me the time!”
The phone hung up and I began crying again whilst R left me at the train station at about 8pm. About twenty minutes past until R came back, crying and blaming me for things and threatening to kill themselves and I had to stop them from walking onto the train tracks.
In the end I had to support them.
This present day R regrets what they have done, I learnt that R went to a counselling session – where they suspect that R has borderline personality disorder. However R is prone to delusional and emotional outbursts where they are emotionally abusive, acting completely heartless, and is possessive and very jealous and insecure.
I told this situation to our boyfriend (as we are in a polyfidelity relationship) and he was in disbelief.
On Christmas Eve, she wrote a status on suicide after breaking up with me, saying her family would not accept me because I could not make it to a Christmas dinner (Despite going to every single event of theirs). My heart was broken and as well as our boyfriend’s. She ruined Christmas Eve by wanting to be completely self-destructive and destroying everything everyone had built for her.
It was only hours later I managed to talk sense into her and then we all went to a café together. It was then decided from there we would all continue dating.
Despite R’s outbursts, R is a very kind and gentle person and I love them very much, however I don’t know if it is the right choice to be dating them.

Many say that R isn’t good for me, but R has been getting help and is willing to change and it would hurt a lot to break up with them – as we have created stories together and many memories, I am extremely attached to them (and I am not sure if this is because I am also being suspected of having borderline personality disorder). And I am also very scared to lose our boyfriend if something were to happen between R and I.

Hello RubySapphire: I'm sorry I don't think there is much I can offer here in the way of advice or opinions. Hopefully there will be some other members, here on PC, who can share some of their experiences & perspective. However I noticed this is your first post here on PC. So... welcome to PsychCentral! I hope you find the time you spend here to be of benefit.

May I suggest you introduce yourself over on PC's New Member Introductions forum? Here's a link:

https://forums.psychcentral.com/new-...introductions/

There's a lot of support that can be available here on PC. The more you post, & reply to other members' posts, the more a part of the community you will become. Plus there are the chat rooms where you'll be able to interact with other PC members in real time (once your first 5 posts have been reviewed & approved.) So please keep posting!