My5boys, you and I are are almost the same. I have four boys and this time last year, my precious newborn girl died of SIDS.
FWIW, my dd was in bed with me, when she died. I didn't notice she had stopped breathing as I had drifted to sleep, despite not intending to. And I honestly don't think that when they die like that, that there's any struggling to breathe, my dd didn't struggle at all, I think I would have felt her. She and your little boy most likely just forgot to keep breathing. You really didn't do anything wrong.
You won't "get over" it, how could you? But as time goes on, it really does get easier to bear. The waves of grief still wash over you but not so often as when you first lose your child. I have found particular dates very hard, New Years Eve, as I felt I was leaving her behind in 2011, her birthday in August and of course the anniversary of her death.
Do join us bereaved Mums on our thread "You light the skies up above me" We have all been right where you are now, facing the abyss. and we are all still here.
Much love to you xxxx