I think writing him a note or email or letter would be a good idea. This way he'll have the chance to re-read it and think about what it says. Try to explain to him that you can't really help the way you were, i'm recently finding this out with my boyfriend who has bpd. Explain to him how you feel now and how you regret what you did. If he has feelings great enough to forgive you and accept your borderline then the two of you can start to deal with it when that time comes. If he cannot accept you and be willing to help you then perhaps it is a good thing he is your ex. Goodluck with it all!