I am so sorry to hear about your wife and all you have been going through, Lee, but please don't give up. I understand the sense of loss and the shock you must still be in after this terrible event, but even in cases where the person we have lost died a natural death, we all experience guilt and such deep pain that we don't know how to bear it, but somehow, if we persevere, we do. You can always find something to feel guilty about. Everyone thinks 'if only I had done this or that, then this wouldn't have happened' but that isn't how life is. People who are so depressed they are contemplating suicide will likely do their best to hide it from those closest to them in order not to burden or hurt them, but they are not in a their usual state of mind and if we don't know, we can't help. This was not your fault and you should not blame yourself for it.
Grief, especially after a loss like this, is always the worst experience of your life and is probably the hardest thing you will ever have to go through. I have been through it several times now for different friends and relatives. My experience is that it doesn't get better unless you make an effort to work at it. I found help in walking and in fine weather, sitting in the park to try to absorb and come to terms with all that had happened. Being in a calm beautiful place, where I could look at the trees, flowers and the grass and water, just somehow calmed me and reminded me that there were still beautiful things in the world and helped me feel a little better. Having flowers around at home helped too. Their beauty and scent reminded me that there were still things worth living for that I could take joy in. It helped just to get out of the house for a walk too. It also helped to meet up with friends for a coffee and I also took up a new interest and joined a class. That helped by getting me out of the house on regular basis and forced me to engage with life again and think about something else. I also made some new friends there. What I was doing was making a new life for myself in a small way and giving myself something to look forward to and a break from grieving, which is exhausting and will drag you down if you let it. You have to fight that, I found.
It's harder to do these things in the current crisis, but there are still on line classes you can join and there are groups like this, where those who have been through a similarly difficult time can offer advice, sympathy, empathy and in the early days, for me, that meant a lot; just knowing others understood and cared and were there, willing to help,made a difference and helped me feel less isolated and alone.
You can still go to your GP and request grief counselling, even in these challenging times. That might be worth doing. Talking really helps. In the absence of that option, it also really helps to write down how you feel about all that happened. Some people find it helps to do this in the form of a letter to the person they have lost, so they can say all the things they might have liked to say to them when they were still here. In any event, it helps to write it down. It really helps you feel like you have got it out of your system a bit somehow, so I would recommend you try. I did that and I also started keeping a diary, writing down how I felt every day. It did help give those feelings expression and as time went on helped me see how far I had come, when I read back over those entries once I was further down the road.
It's a difficult journey for us all and often you make a little progress and then have a bad day or week again, but these do pass and slowly, you do find the bad days are gradually outnumbered by the better ones, so please, don't give in. You can move forwards and you do have a future, however impossible that may seem at the moment. Those of us who are further along in this horrible journey than you, will tell you the same. Look for the little joys in life every day. It could be something as simple as seeing a flower or enjoying a cup of tea, or even managing to get up and get dressed, but each is an achievement when you are under such stress.
Be patient, and be kind to yourself. Life has dealt you a terrible blow and you can't save your dear wife's life now, but you can still save your own and I promise you, that is worth doing. Don't give up. There will be better times ahead. Sending you a hug and strength.