Well, he was admittedly in something of a bind, since Gordianus' later tendency not just to free Bethesda but also the slave boys he encounters (he adopts the later) owes something to a run-in with Marcus Crassus which hasn't happened yet. Also, he has another character ask Gordianus how he can be sure Bethesda didn't run away, that she wants to return to him or that it even makes a difference to her who owns her, and young Gordianus realises he can't know but clings to the conviction she does have feelings for him, which is later somewhat validated (and also if you've read the other series of course by the awareness what she'll do once she's free). However, it would have been possible to give Bethesda more scenes aside from the question of romantisizing master/slave relationships. Though admittedly the first person narrative means we can't get any where Gordianus isn't present, but still.