He was over it. Really. He was.
It didn't take much for Bolin to get over things. He had spent his entire lifetime learning to let go; the time he couldn't get that gift for his birthday because they needed to buy food for the week; the time he found out a girl he'd been seeing was only using him to watch Pro-bending matches for free; the time when he learned that his friends from the Triple Threats weren't really his friends at all.
Time and time again, Bolin let things go because he was the only one who could.
Mako didn't let things go. Mako couldn't let things go. He was stressed, Bolin knew, about too many things; big things, little things, and all the things in between. So Bolin decided that he would be the one to get over things quickly if only for his brother who couldn't afford to do so.
Bolin got over things and he did so with a smile and laugh, despite how he might feel, despite how he should feel, despite how much of a right he had to not get over it. Because that's who he was, that's who he is; the man who needs to be happy go-lucky for the sake of a brother who simply could not be.
So when Bolin tells Asami that he was over the situation with Korra, he means it, because he is. He is used to things like this by now; not getting things that he wanted was a part of his life and to dwell on them would just make everything else a whole lost worse.
He's good at letting go. He's great at letting go. He is the champion of getting over things.
So when Asami comes to him, crying about the situation with Mako, he simply sighs and hugs her close, offering her his shoulder in a comforting manner.
Bolin is good at letting go. He was over it. And as he held Asami closer as she sobbed into his shoulder, he thought that maybe he could help her get over it too.