He was going to go bat shit crazy. If he didn't see your pretty face in the next day or so, he was going to murder someone. Whether it be himself or someone else. Not only had Kenny taken Eren and Historia, he'd somehow caught onto Levi's feelings towards you and had the audacity to kidnap you. He hadn't slept, hadn't eaten, he would snap at anyone who ever dared to mention your name.
The moment he gave Mikasa the responsibility to find Eren and Historia in whatever freaky crystal cave this was, he'd rushed to find you. Threatening one of Kenny's men to get your location. As soon as he shoved the door open and found you sitting in the corner of a room, bruised and wounded, hands bound behind your back, knees curled to your chest, head tipped to the wall, barely conscious, he knew one thing. He's going to kill Kenny. Doesn't matter if it's his old man.
He's walking towards you before he can think.