First of all I'm not "defending" him.If you read my posts you'll see that I've put forth everything from "scumbag" to brain injury/disease...and one or two things in between...as possible *explanations*,not defenses.And as for him being "somewhat healthy" it's possible that his heart,lungs,muscles and spine were healthy but his *brain* was not.
And you are correct to observe that people have an inborn instinct to live,that "instinct" residing in the brain.But remember,the heart has an inborn "instinct" to beat in a particular manner.But as you very probably know it doesn't always do so.I,for example,know it from personal experience.
You still didn’t answer the question - what does it have to do with killing the mother of his child?
Why not his own mother if his brain is damaged which you seem to be so fixated on w/o a shred of evidence?