YANBU, in your situation I think you've been very understanding and the point of this thread was to rant and rage so your little boy goes to his fathers none the wiser. What an amazing mum that makes you, especially after the heartache you've been through. Your Ex is a shite though, of the highest order.
My Ex did this to me too, when our little boy was very ill and had been in hospital for months, the Ex's parents had words (told him to sort his head out or lose his inheritance) and he came back to me. More fool me, I never got over his betrayal happening at the worst point in my life and we were together for about four years after that incident. For a year you are doing tremendously well to not still be breaking into tears (I was after a year).
Having been in a similar situation you will still be massively hurt, and for two reasons. Even though your DS is now on the mend, it takes time to get over such an illness, it brings everything into perspective but also makes you realise how much our DCs mean and how fragile life is. Losing your relationship during such a time means you have to give your heart time to heal, 'just getting over it' would have meant you never cared for him properly in the first place. Loving someone, even someone who hurt you so badly, is not something to be ashamed of, be proud that you were committed and loyal.
Your Ex is the one who should be ashamed of his behaviour.
Be kind to yourself sweet, you and your DS are the only people who matter and if I can (eventually) do it, then so can you!