i think this is the central issue.
you are suspicious of him because of a rocky past (what happened?) and he lies in response, and gets defensive. you also say you are "overly paranoid".
trust is essential in a BPD relationship. its essential in any relationship of course, but our loved ones, generally speaking, have an inherent lack of trust in others. sometimes we do too.
my ex and i had the same issue in reverse. she was overly suspicious. i was defensive or even hostile. she was also intrusive (invaded my privacy), and i also hid things. some that were innocent, but there were definitely cases where i was guilty.
its not a recipe for resolving conflict or building trust. ultimately, that really takes two people, but there are things we can do to lead.
what happened in the past?
Well, honestly, our lack of trust comes from our BPD experiences/rollercoaster before I knew what it was. I’ve only learned about BPD a few months ago but it puts everything into perspective.
I guess it’s also a bit complicated for a couple of reasons (I’ll try to be brief!). He was in a very controlling marriage where his ex wife would completely lose her mind over small issues. He learned that sometimes lying (even over really small stuff that would just be easier to tell the truth) would thwart an attack. He’s brought that “coping mechanism” into our relationship.
I, on the other hand, suffer from ROCD, which ironically, is the constant anxiety, doubt, and obsessive intrusive thoughts regarding the “rightness” of a romantic relationship. I’ve had this long before he came along but it definitely hasn’t made any of this BPD stuff easier to deal with.
It’s funny because I know he is often honest to a point of fault (he’ll admit things or tell me things that sometimes would be better off kept to himself). So I know that we will ALWAYS get to the truth of an issue, but it usually takes unearthing a few little lies along the way to get there. He’s never cheated (I hope) but I know he’s engaged in conversations with people and lied about it. When I find out what’s going on, he’ll panic and try to deny it. Then eventually we get to the truth of it.
It just becomes difficult because my own anxiety constantly cause doubt and fear. And sometimes I will completely make up scenarios in my head (“he didn’t reply to my text right away, he MUST be talking to someone else.” “He didn’t sound too excited to hear from me, he MUST be upset with me” “his phone beeped, WHO THE HECK IS TEXTING HIM?”) so it’s hard to know when it’s one or the other...
I agree trust is very important in a BPD relationship. I would like to trust that he’s also not going to wake up tomorrow and split again but I cant ever know that for sure. I’m not really sure how to feel trusting again amidst all the chaos.