[joeysteele]

I think the difference between Dexter and Callum is that it is now clear to most of them all that Dexter is a storyteller but a good and virtually harmless one.

Callum, has a dark side, he is very hard to work out and does have some uncomfortable ways with people,particularly Charlie with his odd, and ininvited often, stroking of the hair or head massaging.
That is likely what Jackie is very unsure of and not happy with as to him, whereas she has worked Dexter out a bit moreand seen he is by and large likely harmless if you take most of what he says with a pinch of salt.

I myself, would rather spend time in the company of Dexter whereas I don't think I would want to be around Callum very long, his explanations and odd way of making a point come across as insincere and uncalled for most of the time.
Especially his getting at Dexter now at every chance when he talks to others,like when talking to Sam for instance.