missing dog = contributing to suicidal feelings?

As a brief bit of history, I suffer from borderline personality disorder & as a result frequently self harm & have suicidal ideations as well as major depressive episodes. 6 months ago my 4 yo dog was hit by a car & run over when she chased a fox across the road - my 6 year old son has blamed me every since. We have since got another puppy who is somewhat of a carer for my son who has teminal cancer (otherwise I still wouldn't have another dog yet)- will at the moment she i missing. I was already in a major funk but it has been 5 hours now & I haven't seen or heard from her despite constantly calling her name, walking the streets looking for her & even looking through the bushes next to my place in the dark. Now is the time that the foxes are out & the time of night that my other dog was run over. My son is blaming me that our pup is missing (I was walking her form the car to the front door & she pulled her collar off & took off somewhere). It is after 11pm here & he is still awake screaming abuse at me. I have cut myself from the stress & am finding it is not enough. I don't feel able to implement any of the skills I've spent 2 years learning, like they just can't help. I just cannot deal with losing another dog so soon.

How do I stop the missing dog from sending me into this spiral where I don't trust myself anymore. I'm scared of what I'm capable of when I feel like this, & know that i"m going to be awake all night stressing about it. I have a psychologist appointment tomorrow morning but right now don't know how to get through the night.