So sorry you're going through this, what a truly evil man. Please please take care of yourself
I haven't experienced cheating to this level myself but I have been a child who watched their mum behave the way your partner is (although they stayed together in the end, PLEASE DON'T do this! My dad has 0 trust for my mum, they only did it for the kids which is wrong on all levels although I know he had good intentions.)
I truly believe the thing that helped my dad the most was writing notes to me everyday, it was the time he most told me how much he loved me & how lucky he was to have me. Maybe try this with your son? Leave him notes on his bed/on the sofa/at dinner time for him? It'll help your brain remember these positive moments amongst all the sadness and hurt.
Your son will remember you as the best person in his life, you are not a joke- you're a human with emotions and a lot of love that has been thrown back in your face. Channel that love into yourself now, sending hugs

