Name changed as don't want to be identified.
Background- Been with partner for almost a year and we are living together. Yesterday he went for drinks with his friends whilst I went to see his parents as they asked to see us but partner didnt want to go.
Today he told me he was going to see his friends. We were meant to see my family so I called him selfish etc and we had an argument.
He told me that it would have been his sons 3rd birthday today (he passed away when he was 2 months due to SIDS). I didn't realise it was his birthday.
And he went out. This was at 1 or 2 pm. I messaged at about 4 and he replied but I messaged at 8 to see when he'd be back and I've not had a reply.
I feel awful but when should I worry?