Relationships are tricky things. They change over time. As humans, we need relationships - friends, parents, lovers etc but so often make a complete mess of them. Drew and Aria's relationship Aria is very much more invested that Drew who still sees Aria as his charge, albeit one he's very fond of. To some extent, at least, Drew has to keep the relationship professional because he has a job to do and getting too personal could put that at risk.
As for Ben and Amara, I'm just writing a very interesting scene about their relationship. It's a lot of fun - well at least to me, but I'm evil