Is this a healthy method for our son (details)?

Our youngest son ped away 4 months ago, it hit us all terribly hard. My oldest, who is 11, is receiving councilling because he took it hardest. Last night, he came downstairs and showed us a notebook, it was a diary he's been keeping since it happened. He writes a letter to Callum every night, basically telling him what's been happening and so on. It was heartbreaking for me to read, as he writes as though Callum's right there. He hasn't told his councillor about this yet but he says he will next time he sees her. I'm not sure what to think of it, would you think it's a healthy way to grieve? Or slowing the process? Thanks for taking the time to read and answer