"Maybe my caused him stress . He leaved me . "

Firstly, I have joined the two sentences because the second is connected to or reliant upon the first.

My apologies. Unfortunately I have made a mistake in the corrections above. The tenses of both parts of the sentence should agree. The differences are subtle.

"Maybe if I cause him stress, he will leave me." or "Maybe if I caused him stress, he would leave me."

The first sentence is all future tense. In the second sentence, although it is something still to happen, it is as if you are looking back on an event that has already finished, and stating the resulting consequence of that event - just as you have tried to do in your sentence.

Lc2n's notebook entry: Jul 20, 2010

Although I am just a young girl, I think I love a boy named Wei Kay.
On March 12th I met him at the subway. Because of the school uniform, I knew he was my senior.  Then we became friends after a schoolmate’s introduction.  At that time, one of my girl friends was in love with him. She knew that we were friends, so she asked me to help her pursue him.  As time passed/went by, Kay and I contacted each other more and more.
On April 22nd, we fell in love, and I really had a good time at that time. Kay is very handsome and gentle. Many girls in our school love him because of his appearance and character, so I am always afraid that he might/will leave me alone.  I am only a common girl. There are many good girls here. Maybe if I cause him stress, he would leave me.
I really love him very much. Maybe I should pay more attention to my study, but I can't forget him .

Again, don't forget to capitalise the first letter of every sentence and the word "I". 
Full stops and commas must be placed directly after the word and not after a space.

Be careful of verb tenses. "As time goes by" is something that is happening now or in the future. However, in the context of the sentence, it should be a past event and therefore, should be written either as, "As time went by" or "As time passed". The passed tense of the verb "leave" is "left", not "leaved". However, in the sentence you are afraid that it will happen in the future, so should be future tense not passed. That is, "will leave" or "might leave".

"I can't forget him" infers that the relationship is over. In the context of the sentence however, it perhaps should be written, "I can't stop thinking about him".

Hope this helps. :)