Im sorry to say this Op , but i think your H is telling lies when he says there is no one else , this seems to be fairly typical . Being distant , declatations of not loving their wives anymore , going through the motions of relate ect .
So , he states he doesnt love you , but expects you to still live there , maintain the family home , presumably make his meals , wash his clothes , and provide free childcare for your son so he can maintain the image of decent family man ? Its a lot cheaper than a divorce and maintenance isnt it .
And what about you Op ? Are you meant to sacrifice the next however many years , not have a relationship , be his free live in housekeeper , just to suit him ? What hes suggesting is ridiculous . In your shoes i would TELL him , not ask , that i KNOW he is having an affair , and that i will be seeing a soliciter with a veiw to starting divorce proceedings .
With a bit of luck it might just snap him out of his ridiculous fantasy . Youve really nothing to lose at this point .