The letter had made Bruce sad, but he'd quickly resigned himself to the fact that she was gone, and forced himself to move on. Not from her, really, but he had too many other things to deal with to waste his time moping over a woman he hadn't been able to commit to. For good reasons, maybe, but he could hardly blame her for leaving him. Still, he had quickly thereafter tracked her down in Saudi Arabia and the entire time she was there, he had used as many of his resources as was necessary to keep an eye on her. To make certain that she was well, to see what she was doing, and just in case something happened she couldn't handle on her own. Selina was tough, but the Middle East was not a friendly place, and... he worried.
Maria was certainly right about the difficulty of returning, although his experiences had been a bit different. He had come home from nearly twelve years away from home, some of them in school, but most of them traveling with out a name, without money, training, learning, begging and stealing if he had to, in his quest to become the best. He spent time in a prison in Tibet, with various tribes in Africa, Madagascar, and Australia, and lived in monasteries, and saw the worst places in the world. He returned to Gotham a different man - one who knew what he had to do, and had the means to do it.
That was what he saw now as he looked at Selina. She had left because of her own problems, but had seen suffering worse than her own. She had worked with people whose lives were harder than anything she had ever known, and it had changed her in ways she hadn't expected, and maybe not fully realized yet, but the changes she was already contemplating, plus the work she was throwing herself into here told Bruce that she had been just as effected by her time abroad as he had. As Tony Stark had.
And, if he didn't miss his guess, as Maria Hill had. The world was a war zone, and for certain people, with passions, it was a war to be won without surrender.
"Some friends never really go away," he commented, hands in his pockets. He wasn't looking at her though. "The ribbon may be tight, but..." Bruce shrugged awkwardly. Even as Bruce Wayne, sometimes he couldn't find the words he needed, the right thing to say. Selina had always been the only one to notice that he wasn't really as smooth as he pretended to be.