Finally there was one lesson where I suddenly realised that I just can't always assume he doesn't understand me or I have to treat him differently. I can just communicate with him like I do with the other kids and if there's miscommunication, I will just work from there. Anyways, miscommunication happens all the time in any context. Why would I need to discriminate our communication.
Onwards, we have had easier time during lessons. Though still feeling stressful before every lesson, i takes less time to prepare myself mentally, and teach more effectively. Today's lesson was especially productive. I can hear him better, and get to remind myself to let him express and talk more even if I might not be able to comprehend his expression. I'm a very proud teacher today. he doesn't want the lesson to end when I have to leave. : )