Hi s_wolf and let me join FF in welcoming you here. I am in the middle of planning for a separation myself so I can completely understand what you're going through.
I am at the point now where I want to separate because I know it is not right to make threats in a relationship.
Kudos to you for realizing in a year what it took me almost ten to realize.
Seconding FF's suggestion that knowledge really is the first step, and you will find tremendous resources here in terms of the information and members here willing to share their experience. Conversations about relationship issues with a pwBPD can be intensely difficult and we need all the skills we can get before going into one.
~ROE