"He is your freedom, and you are his."
Consider the full meaning of this: JMS is reminding us that Londo and G'Kar (or Londo/G'Kar, as some of us stranger minds prefer ;)) is not a one-way deal, with G'Kar giving salvation and Londo receiving it. No. What JMS implies here is that something similar is happening in reverse- that there is something Londo gives to G'Kar as well.
Londo would probably say some Londo-ish version of "Of course I give G'Kar something. I remind him he's not divine, but a mortal being with mortal desires." But it goes deeper than that. However unintentionally and unconsciously, Londo provides the means by which G'Kar finds his own salvation. G'Kar has an epiphany, but remember that he has to trample violently over Londo to get it.
I've written about this at length before, but the central core of the analysis bears repeating: For Londo and G'Kar, revelation and change is always (and sometimes violently) found through the other. For G'Kar, enlightenment came in the midst of a mindrape. On the flip side, Londo's redemption comes in stages and all of these stages involve Londo's relationship with G'Kar in some way. It begins with keeping a promise, procedes through multiple attempts to reach out, and finds a moment of beauty in a surrender of pride and an embrace of repentance.
So, yes: As I said, that line in The Shadow of His Thoughts must be icon-fied! Because, you know, it's just perfect.