sorry to hear this, jack, and shock that this is - and where you are... it is natural to question why, why, why and more questions and indeed may be even anger.
The good news, if it is that, most of us have been through that....concentrate on all the good times and what she brought you.....
The rest will fall in place and there is a lot of experience here to take you through this.
In short, your questioning, exhaustion and emotional drainage is more than natural. Hod it all in there...chat, ask, and share and comfort will come. When? That is a difficult question but it will come as you emerge from these first phases of grief.