I think it would be better English to say "If I had known, I wouldn't be here now". I think it is the past conditional tense - if (in the past) I had known, then I would not be here (now), but either of your suggestions would be understood.

Why don't you have a cat? is correct, as we usually put do or don't before the subject when asking a question, eg, why do you like fishing? or why don't you call me any more?

Greetings .... Here is my first writing, learning to use Italki

Hi all, I'm Marian. It is my first time writing that - I'm nervous! ... I need to learn English, look forward to your help. By the way (?) I used translations and dictionaries.

 

Hope this is what you meant to say - hope it helps!

A difficult story

Whenever a story is told, it talks about an old man, about a child or itself. But my story is difficult, I will not talk to you about a common being, I will tell the story of a being from another world, about an animal from another universe. It is a story that has to do with the destiny of the Milky Way. This story was hidden for eons. It is about a being from nowhere that travelled from world to world looking for (?) life or looking for (?) death. That will never be known.

first line

Today i start to write my diary in itaki

 

Either Today I started to write my diary in italki;   or

Today I am starting to write my diary in italki.

Can you please correct these sentences. Thanks. №39

Taking into account the rashness of most of his actions, he seems to be a very lucky man. Just remember his half-month trip to South Africa. He was totally unprepared for it and ran into trouble with strange local laws.
As I anticipated, he has flatly denied this. But what I really didn’t expect is he is ready to ask some of his friends with experience in business to answer to my questions.
Upon my word<em> (quite old fashioned!)</em>, I wouldn’t leave the house if I wasn’t fully confident that everything would be ok and there would be no danger for her. At the end she looked quite well when I went home.
You can not refuse this reward. I am sure that you completely merited it. If you don’t think so a better way to dispose of this money is to transfer it to a charity.
I have to apologize. During our last talk I said many things about your way of life, which I sincerely believe to be true. By no means I had intended to offend you, but I strongly advise you to begin a new life, work harder, do some sports and sleep a little bit more.
He is a very well-educated person, but when it comes to discussions he stubbornly adheres to his point of view and concedes no other opinions.
She considered it an indignity, but didn’t show her resentment. Overall everything goes according to her plan and it was enough to her complacency<em> (? can you give a synonym?  Meaning unclear)</em>.
If the flight hadn’t been delayed I would probably have arrived for the concert in time. It was the last concert given by this band and according to their statements in the press, they will never give another concert as a single band. However it is possible that some of them will continue their professional careers individually.
She said this with such unconcealed cunning that everybody began to suspect that something is wrong with this event.