Well, the answer is in your first line. "he has no charm, no talent, no scruples he is no oil painting, he isn't funny so what is the draw? I suppose the old adage is "birds of a feather stick together"
Those were exactly the features that drew Madame to him in the first place. She judged him to be jung, silly, vain and therefore harmless, plus he had that gay/feminine allure she likes so much in men (so that no real man can threaten the gigantic father figure she has internalized). And, as he was so very complying from the very start, so obliging towards each very whim of her, she thought she could easily manipulate him and use him. He also soon became her shield aganist everybody else, so that nobody could reach her so easily.
What she didn't know - being so full of herself and so stupid and so entitled - was that Snorty wasn't so naive and innocent. She misjudged him. Behind that chubby, baby-like face there is a cynical, calculating, cold opportunist who is doing to her what she's always done to others. And he knows too much of her tricks. He has slowly entangled her in a spider web, so much so that now is not so easy for her to set free.
I'm sure she's still convinced that she is the one who's manipulating, but it is not so.
He's the spider and she's the fly.
So, it would be interesting to know if she still has some ways of getting rid of him, like
@Clara says.
Gosh, these perverse dynamics have me glued to the screen!