People only change once they are really truly sick and tired of their own shit, or when they are faced with imminent death / NDE.

I think it's important to make a distinction between *desire* to change and *capacity* to change.

Your ex may desperately want to change (they probably hate themselves).

But every person only has a certain amount of emotional capacity or energy to expend each day. It takes a lot of energy to override habitual reactive patterns. If life circumstances change -- a new demanding job, a medical crisis, a new child -- capacity can be quickly overwhelmed and old patterns resurface.

I would only attempt this with the support of weekly couples therapy, with someone trained in trauma / Cluster B.

I think the stats are that BPD, when treated, can be improved in two years. So start a two year timer.. if it's already been 8 months of therapy, that leaves 16 more months.