tweaking out, cant tell if its the bpd

before i start, YES im diagnosed, YES im an adult

when you get into a disagreement with partner over how a situation was handled in the past (that is still bugging you) and you feel like crap and when you get home and let them know youre still having a heavy heart n feeling like shit n you try to start conversation but they havent answered on multiple platforms only for them to finally respond simply "im on the phone with (friend of theirs they just reconnected with after not speaking to for a year because their ex partner found the friendship inappropriate due to the amount of flirting and sexting between them)" .... i am feeling awful and tweaking the fuck out. cant tell if im in the wrong for having a near mental break over this. feels like a slap in the face because the disagreement 2 hours beforehand was about how i feel lonely and friendless and like partner doesnt really take my side when i need a friend to lean on in my toughest moments. !? cant tell if the borderline is making me unreasonable and im picking up on shit that isnt there.