is it normal to want to leave my pregnant girlfriend

by the way as the name states the mother of my children and i have broken up but not while she was pregnant and in the end the decision was made for the benefit of the kids. i have custody of my kids because after my son was born she slipped into post natal depression. she was just starting to get better when she got pregnant to our daughter after that post natal depression became borderline personality disorder. i'm not perfect in fact i'm far from it and i'm really struggling but every decision i make i put myself into my kids perspective before i make it and i always make sure its for there best interests