The big questions are... Is she currently in meaningful therapy? If so, is she applying what the therapist recommends in her life, perceptions and behavior? Is she willing to do so for however long it take to see improvement, even if it takes years?
In short, something has to change since you're at your limit. So... if she doesn't or won't change then it's up to you to change the scenario.
Just a guess, but it sounds like she has told you she is/has BPD and, more or less, take her as she is?
I just want things to go back to what they were, I can't lose this after everything I've sacrificed, I can't have my son grow up in a separated household like I had to.
Many here have faced your dilemma... a life-changing choice with children part of the equation.
Choice A: Continue the marriage or relationship so the child had both parents in the same home. Problem: Child does not have a reasonably normal home environment.
Choice B: Try therapy to have the marriage or relationship improve and if not then end the adult relationship. Court system assigns details of custody, Parenting schedule, vacations, exchanges, etc. Problem: Child goes between two homes where (as a benefit) one home is reasonably normal.
Neither choice is automatically good or bad. Many factors are to be considered.
