UPDATE 2: I guess there is a little bit of improvement between us. On the first day of school, I asked him, "how was school?" and he replied with "mmm..." I guess that is a tiny bit improvement because he began to start speaking (not quite speaking yet, but at least he did make a sound). Everything is going okay until Sunday when my mom left to Vietnam for about four weeks and he became sulky and depressed all over again. He still hides in the store on that day and didn't want to talk or listen to us. I noticed that he always been quite closely attached to my mom because mom is the only one who is always been there for him and can easily approach him. My mom told me about her leaving to Vietnam and his face went from happy to sad. Since then, I did give him space and back off away from him, but somehow he seems like he had been feeling lonely? Today, I began to approach him and asking him if he wants to eat something so I can cook for him or letting him finding food on his own. I thought he won't respond (he hasn't respond for three weeks now), but miracle happens that he finally began to speak up. There is still awkwardness between us, but he finally speaks up is just a beginning. I will continue to do one more update before I'm going back to college to start school.