I am so sorry for what you are going through OP.
It must be immensely painful and awful to be alone. I hope you feel we are supporting you a little and you are a little less alone as a result.
I do think, though, that you have made a mistake in not expressing your needs clearly to him. He offered to come home and you didn't ask him to. You are wanting him to read your mind or wanting him to want what you want, without you having to say. That's a very natural instinct. But it's really not a fair expectation of him.
He might have loved to come home - to feel needed and necessary to you.... but you didn't ask him. He may have felt you wanted and needed space. He may have felt useless and not know what to say. While I am not saying it is as bad for him, he has also lost a second child. He will have feelings of loss, maybe shame, failure, anger at life .... any number of things. He may feel he is doing you a favour staying away from you. He may feel the need to distract himself with the wedding because he is in the denial stage of grief. Both of you are probably having very powerful emotions and neither of you are feeling able to share them.
I think it is really important that you two start communicating and sharing in this loss together... you will both have very difficult feelings to work through, and the pattern you are setting up at the moment - not sharing your needs clearly and grieving separately, isn't working well.
I would encourage you to talk to him openly. Tell him you made a mistake not to be clear. That you really don't want to be without him at this time and you would like him to come back as soon as possible. Tell him you want to grieve together and you are afraid if you are left alone it will damage your relationship, because it is making you feel unloved and uncared for at a crucial turning point of loss. That sort of thing can cause an 'attachment injury' which is hard to heal from.
My heart goes out to you and I wish you all the best,
Xx