Honestly I am going to just tell you the facts here and I'm sorry if you don't like it but you can control who you are and you can shake the guilt you can forgive yourself and her. Okay with that being said there are ways to go about doing all of that it isn't like the easiest thing in the world especially with BPD but it is possible if you want it. I like many people with BPD have ruined tons of relationships because of this black and white thinking. But the first step of ending this "I can't" cycle is to forgive yourself so once you do that the rest is easier. You aren't a horrible person no matter what happened in the past no one is a horrible person, we may have horrible actions or words but our words and actions are not us as a whole person. No one can pull you out of this but yourself and we are all here to support you through it like I said it isn't easy but you have to want to get better and know you can for any healing to start. I know you have it in you!! Good luck and try to find it in you to start DBT therapy!!