Hi Juan, and welcome to the family. Coming to this site is a great first step on your journey... there are some great resources available and a community of caring people that have shared experiences.
I encourage you to read through the site and the forums, to help you get a feel for what your relationship will look like in the future.
To answer your question, BPD is a lifelong condition. There are coping mechanisms through therapy and DBT that can make a dramatic difference in a pwBPD's behaviors that make relationships much easier. It is critical that the pwBPD want to seek treatment on their own, and not many do. This article might be relevant:
https://bpdfamily.com/content/how-to-get-borderline-into-therapyAlso, many here have read and recommend the "walking on eggshells" books and the more recent book "Stop Caretaking the Borderline or Narcissist: How to End the Drama and Get On with Life".
I would also highly recommend you refrain from bringing up BPD with your fiance, especially when emotions are hightened. Generally people don't like to be reminded that they have mental health issues.
What are you doing to take care of yourself? It is critical for the success of your relationship...