Hello Kelly,
I'm glad you are going to just box everything up. I don't think going through stuff is something it is a good idea to attempt when you are still so fragile and getting over the shock. You do make rash and wrong decisions when you are in that state and should not feel guilty or selfish about it. You have to give it time and give yourself and those around you time. You are all going through turmoil that you cannot comprehend or deal with at the moment and this will only calm down with time.
Don't judge your partner's mum too harshly. Having lost her child, she will be devastated and probably will be looking for an explanation and someone to blame, but you are not to blame. When people are at such a low ebb, especially men, who often feel a duty to be strong and don't like talking about feelings, they hide it well, because they don't want those close to them to know. Like all of us, when we are stressed, we don't always think rationally and make reasonable decisions as we would when we are our usual selves. Sadly, it seems your husband was good at hiding his real feelings and was so weighed down by them that he took this irrational decision that he probably never would have done under usual circumstances. Mental health, depression, stress, they all colour and distort our view of reality and get things out of perspective, in this case, with tragic and terrible consequences and naturally you will play the blame game as we all do, thinking if only I'd done this or said that or known or should have known, but you couldn't because he didn't show or tell you clearly enough. He was probably trying to protect you in his own way. It is not your fault, Kelly.
Acceptance is key. You will mull all this over in your mind for months to come no doubt, but in the end, you have to accept that what happened just happened as it did and if you could have changed it, you would have done, but you couldn't. You were not given the chance, not really. You might think you should have realised this or that, but that is easy to say with hindsight and very different when those events are taking place.
Be gentle and patient with yourself. You are the priority now. You have to live for him too now and when you do meet up again one day, I suspect he will be so sorry that he did whatever he did and will never blame you himself.
Sending you a hug.. xx