Honestly, I think Emiel being overprotective is two fold by this point. One, it's his job- which he failed at once. So he has that baggage to deal with. Two, he broke his promise to her by failing said job. So he has that baggage as well.
He's not exactly putting her in a gilded cage, but having failed a young girl who put all that trust into you... I know I'd probably be worse.
Putting the whole love story aside, as it's meta information anyways, I think he's doing exactly what any bodyguard would do if given that second chance. I mean, given the family, I'm surprised he's still alive- or the very least, imprisoned.