Hey. Sorry for the wall of text. I posted this in relationship_advice and cheating reddit, but I really feel as though it would be helpful to have the opinion with others having bpd. My girlfriend has had a recently diagnosed bpd about 3 months ago and since then she's been making quite a bit of efforts to make the best out of it. We've been together for 4 years now and she had been on anxiety pills for all that time and coming off of it about 4 months ago kind of "revealed" the underlying diagnosis that was bpd. Now this post is about me getting "cheated on" at least by the definition of it. I'm asking here because I wanna know from others with bpd if her behavior is somewhat expected of someone having bpd or if she just simply doesn't respect me at all. As a little background, her mother probably has npd but she's been in complete denial her whole life and caused a lot of issues, like a lot. Many suicidal attemps, manipulation... She had a very hard time growing up and had to take care of her. She's slept with a lot of people, like 60+ whilst me 3. Almost all of them were very self-destructive people, and honestly assholes. On the other hand, I'm lile the good guy golden retriever that she found and I think this whole issue stems from the fact that I'm not intense at all, I'm very chill and that she feels the need to "flirt" and have other people validate or like compliment her or something.. 

Anyhow, here it goes... Basically, I've been with gf for 4 years, have always been faithful and 2 months ago she started writing to pen pals from prison. To my surprise, 1 month after I found out randomly on my old macbook that she was flirting with two of her pen pals. She was very emotionally attached, she was sending old sexy pictures of her on the app, they were always talking sexually and all of that in my back. I comfronted her and "let her" keep talking with the other pen pals besides those two. Since then I've never felt like I could trust her and always doubted everything she said to me when I was asking her if she was still talking to them. Yesterday I checked her facebook and phone, found out that she talked to a random girl on messenger and was talking about "her man" and such referring to one of her pen pal, whom I had asked her to stop talking to. It was extremely hard reading something like this, her referring to someone else like that again behind my back. I comfronted her again and she said she was just didn't want to tell the person that this pen pal of hers she had stopped talking to him and all and that it was easier talking to her that way. How can I trust this..? In her messages she even referenced having rented out a USA phone number to call the guy..? On her phone, on the app I had seen that the other pen pal which I had asked her to stop talking with had written to her on the same day. I didn't check the conversations, just saw that he had written to her on the same day. I comfronted her and she says she hasn't talked to him at all ever since then, it was just him that was trying to contact her back and that she just blocked him since then. She showed me her phone and the guy wasn't there in the conversations anymore. How can I trust her again? This is a lot of coincidence. I'm not proud at all of violating her privacy like that and never have I even thought of doing that in our almost 4 years of relationship. The pain in my chest, the doubt and the stress was just too much and a few times back when I had asked her about it she has said me she never talked back to them but how can I believe her seeing the facebook messages..? And then the one from the app literally on the same day?

What hurts most is that I love her and I really want to live my life with her, but this has become so hard to deal with... She has a recently diagnosed bpd and is making quite a bit of effort trying to live with it and get better at handling it. However, how could that explain such miscommunication? All the time I've been very understanding and have given her many chances to talk about it, I never, ever insulted her and always just thought of solutions to make us happy, thus why I wanted her to keep contact with her other pen pals..

To her defence, what I did is definitely an asshole move to look into her stuff ans thus violating her privacy. She's also just starting to handle her newly diagnosed bpd and has very low self-esteem because she gain weight. However, why would it be so hard to just show your phone to prove that you didn't do anything if it's true? I just don't understand, if the roles were reversed and I truely felt remorse, I'd literally give my phone to her and let her look around for as long as she'd want... Yet I just wanted to see a glimpse of her latest messages to know she wasn't talking with the 2. I literally just want a reason to be able to trust her again, but all this just makes me go crazy that she's so closed on all of this..

This is just so hard, I sincerely believe that she also loves me.. For her, what she did is NOT cheating, for her it's physical. Everyone has a different meaning to it imo, but the end of the line is that you have to take into consideration your partners way of seeing it no..? I've repeated it to her I don't know how many times after it happened, but then that facebook message and the message on the app..? Am I just some controlling psycopath? I've never had issues with this, it's literally that I don't trust her and when I feel stressed about it and have doubts, I ask her to just show me the app so that I can see there's nothing with the 2 pen pals and she always says no saying she's not comfortable because it breaches her privacy. To me this is very understandble under any other kind of circumstances, but in this one shouldn't the other partner be happy to prove to the other that nothing is going on? 

Thanks for any inputs, please don't just post "break up", an explanation of why would be greatly appreciated because I really love her and even with all of that, I believe that she does really love me. Somehow, I really want to find a solution to all of this, even if it'll be hard. What should I ask of her? What am I doing wrong? Should I tremple on my feelings and give her the benefice of the doubt? To what length should she do her part to "make this right"? I just want constructive opinions please, sorry for being so picky, I'm feeling so fucked with all of this. Thanks.