A love hate relationship in Tuition

Having been teaching Aaron for 4 years, sometimes I just feel so disappointed in myself. There seems to be like not having any improvements at all despite all the years of teachings. I think the greatest joy so far is to see the change in his attitude towards studies. I can see that he is very determined and the willingness to learn. However, I just can't seem to teach him to understand the concept fully. Sometimes, he don't even know how to answer a simple question. Which I feel very frustrated about it. I am already very patience but i guess i just cant really communicate and enter his world. I am really very tired. I really cannot cope in teaching him 4 subjects. The most i can teach him is only 1-2 subjects .Perhaps I am not the right person to guide him or he should get a real proffessional tutor. Contrary to this, Aaron has been a good student. He never fails to finish my homework and is very eager to learn.Despite his occasional tantrums, he would always apologize in a very sweet way that i felt so bad for scolding him. It's such a tough decision whether to give up or continue to teach. Next yr it will be his N level and I doubt I have the ability to help him. Perhaps I should just give up and leave him to a professional .