Why do I still feel like this? It started three years ago and was much worse, but it got slightly better after a few months all of the sudden and hasn't changed since.

Sometimes situations take longer to heal than others. One time, for instance, I had fallen in love with a girl in the eighth grade and was expecting the one-sided love to be over within a year or so. On the contrary, another year passed, and another year passed, and I still liked the same girl. By that time, we had already quit talking and I was pretty down about it. After all, the situation was much worse and she had gotten a boyfriend. Nothing in my life for two years seemed to work for I was so focused on her. Finally, I found a way to solve the problem after two years of waiting and it was simply reaching out to her and explaining my feelings. After all, I was not trying to interrupt her life or relationship, but only fix mine for the better. In the end, she understood and I have happily moved on from such dark times and been quite successful in my pursuits. In essence, I cannot give advice. I am not even sure what your situation is. But what I can say based on personal experience is that if time does not heal the problem approaching the root of it directly just might. Have a good day-- don't forget that you are an amazing person!