Happiness, Bane knows, is an insubstantial object.
For some people it seems to come so goddamn easily. For him, he can only catch glimpses of it from achieving his goals. If his goals involve hurting people and toppling governments, well, that's just collateral damage.
It was hardly his goal, the whole toppling Gotham's judicial system, but it was her's, and of course, he'd follow her anywhere. She was smart, he was deadly (and ruthless). They were a good pair, or at least he thought so.
And it wasn't like he didn't agree with her. He was a killer, without mercy, without thought for consequences. He did what had to be done. And he never did blindly follow her about like a trained ape. Even the greatest minds needed to be reminded every once in a while of the impossibility of their schemes.
Yes, they were taking down a city, and no, he was not sorry.
And he wasn't one to accept defeat either. Mostly because it didn't come to him very often.
He knew from the beginning happiness may or may not be waiting for him at the end of their endeavor, when Gotham was in ashes. He convinced himself that when she was happy and satisfied, he would be too. Or maybe that he didn't need to be happy. It's not like a man with the kind of power he possessed needed to give a shit about anything. He's practically superhuman.
He doesn't need a perfect life, he just has to make sure she gets a shot at it.