ANSWER:
There’s no marriage without the consent of the woman’s wali, even if she’s a widow of whatever age, otherwise this would be considered as zina.
You must stop all communications with this man immediately as he’s not your mahram and what you both are doing is haram.
He must propose to your son asking for your hand and a proper nikah with your wali’s approval and in front of two male witnesses must be performed for it to be valid. Secret marriages are not valid!