Much as it hurts him, your husband can not possibly say that he will be on his own...............he might meet a lady friend very quickly and against all expectations find that he enjoys all this new attention !!
He may well find that actually he likes living alone and will embrace all those nerdy hobbies he would like to have done but didnt.
He may hurt but always want to be in your life....................... but if you are to let him stay in your life, then you have to learn not to put everyones elses needs before your own.................. ie. dont give up just cos it could possilbly make him sad.
however, at some times in your response, i wondered if you really do want to leave - you were upset he told his mum...........why ?? this is what you want isnt it ? you cant get extra work because you look after you grandson - dont you think thats a convenient to allow you to not have to do what you keep thinking or saying you want to do.
I dont know your circumstances, but if you split up and have a low or no ncome then you would be entitled to housing benefit etc etc............................. you dont have to stay unless you want to - be very clear on that, if you really really wanted to you could be out in a week ...................
So be honest with yourself, if its not what you want - then what do you want really ?
Best of luck