Is everyone obligated to follow the fatwas of his country, and if we adopt the fatwas of scholars of other countries, is it considered a sin?

All perfect praise be to Allah, The Lord of The Wolrds and may His Peace and Blessings be upon our Prophet Muhammad and upon all of his family and companions.

It is permissible for the person who isn't specialized in Sharia sciences to apply the opinions of renowned scholars whom he trusts ,whether they be from his own country or not ,but if the scholars have different opnions regarding a certain issue/matter, then he must consult someone who is more knowledgeable than himself .It is preferable that you (the questioner) specify the case of your interest ,so that we could give you a more specific answer since some scholars deliver fatwas based on illogical/atypical opinions which should not be applied no matter what .And Allah The Exalted Knows Best.

Is Fajr (dawn) Sunnah a confirmed one?

All praise be to Allah The Lord of The Worlds                                                                                                                                                                                  Of course, it is a confirmed Sunna which the Prophet (PBUH) used to offer in a regular basis. And Allah Knows Best.

What is the ruling on the chatting between a young man and his girlfriend?

Private chatting between the two sexes entails religious violations, and leads to prohibited attachment.

I placed my hand on the Quran and made an oath to avoid doing a specific matter, but the devil seduced me. What is the ruling on this?

You are obliged to pay an expiation; feeding 10 poor and the cost of feeing one is half JD. And Allah Knows Best.