John is so bad at relationships. He couldn’t keep a girlfriend; didn’t get married until his mid-forties; doesn’t talk to any of his family and Harry didn’t even come to the wedding; all his friends hate him; the one serious romance we know of before the show started crashed before it even really got going very far.
And then he married Mary and it was two-fold:
He is in a Heterosexual relationship with someone Normal.
He has managed to actually have a relationship long enough to even get married.
And now he knows the first one is false because Mary is far from normal - She wasn’t supposed to be like that.
But the other one is false, too. It was Mary’s job to marry him. John didn’t finally succeed in having a relationship. Can’t wait until he finds that out.