I love writing Ambrosius as a total simp! He's... Simprosius! But now, consider...
Ballisimpster!
because I totally believe he's as equally devoted to Ambrosius as Ambrosius is devoted to him
After his bathroom ritual, as long as he was around, Ballister would take to brushing Ambrosius's hair.
This is because while he's sometimes annoyed with the long baths (and that's only when he's unlucky enough not to go first and has to wait. Otherwise, he's affectionate about it), Ballister still knows it's important to Ambrosius.
Early in their live-in arrangement, he would hear Ambrosius wonder and worry if he was brushing every part right. Ever since, Ballister does it when he's home after Ambrosius's bath just so he can put Ambrosius's mind at ease and helps him brushes his hair.
Ballister would massage the scalp a bit before he starts blow drying it with the lowest heat, because yes it takes a while but Ambrosius worries too much heat would be damaging.
If the hair is long, he also braids them.
Ballister definitely memorizes all of Ambrosius's allergies and if that ain't simp energy...
Ballister also knows how Ambrosius likes his food and drinks.
Ballister would stop Ambrosius from going off on Todd for insulting him, but if Todd insults Ambrosius... Ballister would absolutely ruin him in a spar.
They also didn't like Ballister much in training days, but the rest of the trainees in their batch definitely thinks Todd should learn his lesson about messing with Ambrosius.