Char keeps everyone at an arm's length and isn't one to form close relationships unless it is to his own personal benefit or toward a greater cause. "Something something Char uses sex only to get what he wants." It's little different with Bright, even if Quattro isn't quite sure what he even wants out of him. It is that distance why I see ChaBri as an on-again off-again relationship during their wartime tenure; one certainly strained by developments of the Gryps Conflict and wherever Amuro is concerned. To Quattro, Bright is just a convenience; someone who could help fill a small part of the gaping void when needed most but who can't possibly completely understand him. Bright is second fiddle, a means to an end, just as everyone else before him. And he certainly won't be the last.

Bright is smart enough to know he is being used in that regard. And it hurts yes, especially so fresh after his separation with Mirai. (My personal preference with my ChaBri ship is one where Mirai and Bright, strained by the escalating militarization of the Federation driving a wedge between them, choose to separate.) But there are far more pressing matters to concern himself with. In the same light, having already separated from Mirai and with the ongoing Gryps Conflict and the emergence of Neo-Zeon, even Bright has to question if he could seriously commit himself to any relationship again. And that maybe he too is also benefiting from his and Quattro's transactional affair. In the end, they are both empty men trying to make due with what they are given, yet neither can truly complete the other with their conflicting needs and values.

I believe that Bright and Quattro would've eventually split off, had Quattro not gone MIA at the end of Zeta. Nor can I see Bright pursuing another relationship thereafter either, instead devoting (resigning) himself to his work with Londo Bell. At least there is a degree of assured stability and control with that.