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I will say it doesnt matter for daily life and no difference, but it will be new negotiation topic for you. That´s why i dont say anything...

In suitable circumstances they can both be translated with ´always´ but there is a difference.

Artık is a very handy little word. It always denotes a change in the situation, a turning-point in the course of action. In your example sentence 1 says the speaker did not live with his wife before but now he does. Sentence 2 does not take a stand on how things were before.

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I wonder, for instance, when it said

yazma artık

can be used artık for stressing the negative....?

thank you

Artık here functions as an adverb rather than "stressing",  in this context it means "anymore" . On the other hand, it does effect the verb as an adverb. 

"yaz + ma" 

yazma artık ---> Don´t write anymore.

can I ask for another example

çok teşekkür ederim

Tamam , sor .

anlamadın sanırm..

senden başka bir örnek istiyorum, lütfen, anlamak için

teşekkürler

What if we use it with a positive verb ? 

Yaz artık ?