Opinion/thoughts always changing and it's exhausting

Hello, I don't really know how to start.

My therapy is currently on pause because of the pandemic and we have analyzed, that I have Borderline Personality Disorder characteristics. (Minus the anger outbursts)

To make it short, my opinions or thoughts are always changing drastically.(The most problems I have are in things like relationship)
It literally feels like on the one day I have person 1 thinking and on the next day or hour I have person 2 thinking. I am sorry, I'm not talking about Multiple personality disorder, I just don't know how else to explain this.
I mostly know how to ignore irrational thoughts like "Oh my friends haven't replied to my message for an entire day, it must be ecause they secretly hate me." It feels like something completly different and more powerful, which exhausts me because it's so intense. It's really exhausting because I don't know when I am the real ME or when is it just an irrational phase, it feels like I can no longer trust myself and my judgement because it shifts so easily...

I currently feel like I am unable to lead a healthy relationship because of this and some other things I want to work on. But I really don't know, should I first work on myself via therapy or do you think it doesn't matter and I can work on myself in a relationship?

I plan to talk to my therapist about this but don't know if I can change this or is this just the way I am and do I have to life with it for the rest of my life?
Did anyone experience something like this, or does someone have some tips how I can change this?