As awesome a mechanic as that would be (and let's face it, your character would deserve it), when doing the same thing with the mother, there is a random event where you get the option to apologise, which boosts the love stat back up.
It takes (in previous versions) a couple instances of that event to fire, before being able to resume "normal" business with them again.
Instead of forcing, just dose her up at the weekends whenever she stops gaining lust from certain actions... Like a "good, non-rapey mind altering ethically challenged mad scientist"