* Not a teacher
Your text is very well written. I have a few suggestions, though.
I walked through the city park, which was empty at this time of the day, but for dog owners and their pets. I came to the path close to the river and sat on a wooden bench. The river had swollen because of the rain and its colour turned into dark brown. A few boats moored on the other side bobbed on the foaming waves. It was silent but for the water hitting the wooden planks, which protected the riverbanks.
I opened “My Testimony” and managed to read only two-three pages,- (I wouldn't use a comma) when I heard shuffling of the shoes on the gravel. I looked up and saw a plain woman in her thirties with a short blond hair. There was a strange expression in her eyes, detached, as if she was looking at something beyond our world. It seemed to me that - (I would definitely use that) she was not aware where she was walking.
She kept my attention just for a second or two and I returned to my book. I heard the crunch of her heavy footfalls passing by and then they stopped. I looked up again and saw her standing a few meters from me. She seemed to be pondering on - (it is optionally) what to do next, - (no comma) and then, suddenly, she turned around, strode towards me, and without uttering a word sat down on the bench. I had been sitting on this very bench for years and it seldom happened that someone kept me company.
Occasionally, old pensioners would sit down, rest their hands on their sticks, breath heavily and complain to me about the costs of living, their health problems, their children who did not visit them
him- (you said "their", plural) anymore, or their would lament that they could not recognize their own homeland anymore.
I turned again to my book trying to immerse myself in the fate of Mr. Marchenko and millions of his compatriots, but the presence of the woman had spoilt the pleasure of reading. My eyes pored over the sentences, but my mind refused to retain any information. I felt a kind of negative energy emanating from her. I cast her a few furtive glances and noticed that she was completely motionless, staring somewhere in the distance. She wore a black parkas, blue jeans and brown scuffed shoes. An ordinary woman, one could see in their hundreds every day without giving them a thought. But still her presence evoked a strange feeling inside of me.
Something was telling me that she did not feel well. I could almost feel her pain. Her unhappiness was so great that it gave me goose pimples. I could not take my eyes off her. She must have felt my look on her, because she turned her head towards me, watching me with her grey, glassy eyes.
“I can sense that you don’t feel well.” I said.
“I’m going to kill myself. You’ll probably be the last person who has seen me
myalive,” she said. She uttered these words without any emotion, as if she was talking about bad weather or some other banality. Some other person would have certainly winced at her words, but I have seen so much blood and killing in the war that nothing could surprise me anymore. I had also some acquaintances who eventually commit suicide and I always believed that killing oneself is the act of utter desperation. A person could not fight anymore. He or she has been suffering so much and they have not seen any other way out. The pain was stronger than life and in the end, the pain won.
“Is there no other solution? You’re still young, things can change.” I uttered these sentences before I became aware how stupid they must sound to someone who was so desperate that she had decided to end her life.
“I’ve been waiting too long. I can’t wait any - (leave it or not, it's just a matter of style) longer. My life won't
notchange to the better.”