I doubt the maid would go full yandere. I see her as more the seduce the master while she is ovulating type. But with her mother and grandmother working for the family I assume she would know exactly how an unwanted pregnancy would be dealt with.
She says she finds it unbearable and that she wants to run away...But I think that's just her feeble attempt to deny that she actually enjoys her job there. And her stopping him from sexually harassing the other maid, too...Was she perhaps jealous? Wanting him to do that to her? Intriguing.
That ending though. Bah, betrothed? That's no excuse to not pay attention to such a lovely maid that attended to you for so long. And as for what she meant by that ending...Could she perhaps have finally realised that she chose to stay and not run away...for a reason?
On one hand, the art is gorgeously faptastic & there's no actual rape. On the other, the MC is a douchebag ouji-sama type that I despise & the nice meido-san is too weak-willed to do anything about changing status quo so it goes nowhere.