I always viewed it as platonic, father/son-type bond.
The parallels I see with the Carrie/Brody relationship are taken directly from Carrie’s mouth: she pulled him apart and put him back together as someone else. Not literally of course, but I actually think Carrie dismantled the idea of “Brody the terrorist” and rearranged the pieces so they would resemble something like “Brody the hero” (in fact, this is exactly what she does in “Q&A”). Weirdly, Nazir kinda did the same thing, just in the opposite direction.
I also believe Brody loved Carrie out of necessity, “the way a “drowning man loves a slowly-leaking life preserver.” Did he love Nazir in that same way? I’m not sure, but it could be argued. Carrie and Nazir both held his survival in their hands and ended up using him as a means to an end.