Found out my partner is cheating on me

Hi everyone. For anyone who has BPD and has cheated multiple times, what have you done to change? And what urged you to make that change?

As from the title, I just recently found out that my partner has had another girlfriend in our 6 months of dating (with 3 months of being official). I've done a lot of research on BPD because of my partner, and I, having some traits of it myself. We have talks about his BPD all the time and I have been patient and understanding of his issues. He's always expressed his want for change and to become better. I try to help him by researching on the topic while we're together, encouraging him to journal (we also have a shared journal), giving him reassurance that I love him and I'm here to stay, and just being vulnerable with each other.

He's also had another instance of cheating before this and I'm afraid that he may be a serial cheater. He owned up to the instance before and we were able to work on it in a healthy way. He would always reassure me that he wasn't talking to anyone else and that he was too afraid to lose me to do it again. Now that there has been another instance, I don't think I can trust his word anymore but as stupid as it sounds, I'm still committed to working on our relationship. His reason for cheating (the first time) was because he said he was afraid I'd leave him (and many more in relation to his BPD but never used it as a reason). I don't want to leave him at all. It hurts a lot but I believe I'm secure and patient enough to work on it with him.

With that being said, I would look forward to hearing your experiences regarding this. And if anyone has had a similar experience and is still together with their BPD partner, how did you both overcome it? And if anyone can recommend online DBT services, I would be grateful.