Back story:
I've been with my boyfriend for 16 months. He's really the sweetest most caring person ever. However, when he feels cornered he lashes out in very childish ways. Basically his anger reminds me of a child being angry in terms of how he expresses it. I spoke to my therapist about this and she said that first of all this is possibly a result of his own traumas, but that this is also extremely common in relationships between a BPD person and a 'normal' (or at least currently undiagnosed) person; when the person who was unstable earlier start to sort themselves out, the partner reacts by exhibiting the very traits the pwBPD just started getting rid of. Indeed, I do relate strongly to his "childish anger" but up until now I've just found it strange of him to suddenly express in these ways.

Has anyone of you gone through this? How can I help someone who's suddenly "turning borderline" while maintaining my own new found kind of sanity-ish-ness?