This is the ending for my story above. I find it so hard to write in Vietnamese, so this will be written in English.
***
03/12/2017
I arrived at the restaurant where the wedding would be held. There she stood in the hall, smiling cheerfully while greeting the guests. Next to her was her soon-to-be husband and their parents. Among all of them, I knew nobody but her, only her.
She looked beautiful and happy. Her white dress was a perfect fit, making her even more charming. I bet almost every man would fall for her, as I did - but that was 6 years ago.
That day I came, my mind was a mess. I couldn't even know exactly what was going on my mind. But I did know I didn't feel happy for her at all.
The wedding ceremony was a typical one. As it was proceeding, I tried to recall all the memories we had together. But it already started to fade away.
And as I wrote these lines, even the memory of that day were becoming more and more blurry.
Until the very last minutes of the wedding ceremony, nothing really happened. I just stood there, holding a can of beer while watching some of my friends who came with me taking some photos together with the bride.
I thought I could finally put to rest all the memories and I wouldn't need to recall them ever again.
Just as her parents were leaving and passing by me, her mother called me:
"Are you [my name]?"
"Um, yes" - I answered hesitantly as I was caught by surprise.
"Oh I see. I heard a lot about you from my daughter!"
"..."
I was speechless and froze for a few seconds.
Up until then, I had thought that I wasn't really significant to her despite being so close to her. I had thought nobody related to her would know me. And she never said that she told her mother about me. To the people around her, I was pretty much invisible. I took it as a fact, since I knew if those people became aware of my existence, things might be difficult and complicated for her. Sometimes I wondered if I had left any impact on her. Well, I should be just an outsider, and I accepted it. 
But then I realized I was wrong. I didn't know she would talk that much about me to her mother. I didn't know the importance of my own existence to her. I underestimated my own ability.
For a moment, I felt so proud and glad to be such an important person to her.
And then I thought, what if I had tried harder? What if I had really pushed forward? What if I had been more active? What if I had loved her more? What if I had made her realize how much I loved her? Had I succeeded, would I have been the groom standing next to her there?
For a mere moment, all of those thoughts flashed into my mind. And then they left as quickly as they came.
The very next moment I knew, I felt utterly bitter and disappointed. I knew I was such a coward. I was afraid of failing and losing her, as I did twice in the past. I knew I was such a trash human being with no life goal, no motivation whatsoever. My soul was long tainted. I knew I could never deserve such an angel as her.
And I knew too well the very first time I was acknowledged by her family would also be the last one. I was given a chance, for 6 whole years, and I failed.
I wished I could cry.
A few seconds passed, and I was still standing there with a smile on my face - the kind of fake smile people would always see me wearing. The last thing I did was to say goodbye to her parents.
As I was leaving the hall, her younger brother, whom I had met once before, came to me. He walked beside me and tapped my shoulder lightly as if he understood everything - well, perhaps he was told about me by his sister, too. I remained silent.
10 years, 20 years or so from now, people will probably forget most of it. Even if I want to hold on, it would eventually slip from my grasp. But this feeling of sadness would always remain.
Everything truly ended this time, finally.