Hi Their Dad,
You've been through a lot -- and it's confusing to still feel attraction to someone who can be so toxic. Often these confusing feelings go back a long way, to conditioning in childhood where we first learned what it meant to be in intimate close relationships. It takes a while to recover and heal, not to mention some time and support. With kids involved, it's a different type of recovery, and slightly different tools to manage the impact of BPD on the kids and two households.
You're in the right place. People here understand what you're going through.
Some of what you describe is straight up grief. Have you looked at the
Lessons on the Leaving board? It really helps to know that there are stages, as well as milestones that others are working through. Also skills. You'll learn a whole new way of being yourself in the world, much more healthy. This is something you'll be able to pass along to your kids, who need your help.
A book that really helped me (I have a S13 who was 9 when I left) is Bill Eddy's book Don't Alienate the Kids. Even if your ex has not started the loyalty binds with the kids, there is a good chance she will, like whirlpoollife mentioned in her post. The book does a nice job of describing the attachment issues at the root of healthy/healthy human bonds, and how that impacts your ex, you, and how you can help your kids develop secure attachments. It also made me realize how much my son was going to need me to model what it means to be emotionally healthy. Best journey I've ever been on.
Divorce is painful, and divorce with a BPD ex even more so. I echo what whirlpool said too about doing something for yourself, even something small. Every day. It's important that you take care of yourself in some small way to break the constant stream of negativity coming your way, including the negativity you may be pointing at yourself. Someone has to look out for you, and you're just the man for the job.

Everything else is based on this. It just is.
What kind of custody arrangement is in place with your kids? How are they doing?