Part of my healing has involved going back over the relationship, especially the early days, so I can understand what happened, what the red flags were and where my part in the ultimate dysfunction came in so that I can make the changes in me to never find myself in that situation again.
Background, I was with my ex for almost 15 years. The first year was textbook BPD perfection... .fast moving, lots of emotion, lots of sex and both of us were fresh out of our first marriages. I was 6 months out and he told me he was "awhile" out but I found out years later he was 3 weeks out when we met.

#1. The next few years were a little less intense but at the 4 year mark, we had a child together after buying a home together. Our daughter was about 18 months old when we got the devastating news that his son from his first marriage had disclosed sexual abuse in his Mother's home by his 2 stepbrothers. We were informed of this on a Friiday, and by Monday, I had us in court trying to get custody. My ex became like a turtle on his back at that point and couldn't cope with anything so I did everything both in the home, and dealing with social services (his son had been placed in temporary foster care), the lawyer over the custody case, and gradually, everything related to taking care of our home.
Because of the trial over custody, we decided to get married to make our home look more stable. It wasn't a priority before that point, and looking back, I think this was the tipping point. Our wedding was ultra casual, with just my sister and her husband and our kids as witnesses on the dock of a lake we were camping at, and then a "reception" for friends and family as a bbq at our campsite. Again, with hindsight, I now see how this was overwhelming for him. He had the first full on rage ON OUR WEDDING DAY on the beach at the lake, throwing his wedding ring at me, throwing stuff around our campsite in front of guests and our kids and storming off for hours. I'm assuming now with what I know about BPD that it was the engulfment of us actually getting married that caused it.
The next 7 years were filled with raging, with gaps anywhere from 3 weeks between rages to a max of 6 months. Looking back, I believe the news of his son's sexual abuse sent him from higher functioning BPD or just traits to full on symptoms. Does this make sense?