I don't understand why does America needs "guard dog" in middle east and why does it want destabilization there?
An stable region means countries with vast amount of resources would be able to advance in different fields. For example see what China has done to US industries, imagine if an entire continent did that.
Why isn't there a war between America and Saudi Arabia, Qatar, etc?
Roughly 20 years ago they started a war with Iraq, Afghanistan and Syria. That cost them about $10 trillion.
If they can pull a soft-colonization on Saudi Arabia, etc. without shooting a single bullet, obviously they'd choose that!
Why didn't America destroy them and steal oil instead of paying them billions of dollars and letting them to build one of the greatest countries with modern infrastructure and modern everything? Couldn't America and Iran, Syria, Palestine and some other countries befriend with America and develop as beautiful countries as Saudi Arabia is? I don't understand this part, why is there a war between them instead of partnership where both benefits?
I'm not sure what you mean by "modern infrastructure". A country like Saudi Arabia is riddled with poverty and is far behind in development for basic infrastructure in majority of the country.
Don't just look at Mecca that is basically a "tourist" place they've developed because that is the picture that would be broadcast to the world. If you go a couple of blocks over, people are living in ruins.
Not to mention that Saudi regime is a dictatorship that doesn't even allow basic statistic about the situation in the country from coming out and nobody dares report on it either after what they did to the Washington Post reporter (chopped him up into little pieces).
Btw do you know why does Syria and Hamas recognize the independence of Abkhazia and South Oseti? Is that because these countries want a good relationship with Russia and do things in their favor?
Of course. In this world there are only hegemonies that exert control and dominance then there are other countries that accept being dominated by the hegemony to try and seek their personal or national interests under its shadow.
For example United States is a hegemony and Saudi Arabia is basically its colony. US dictates its policies and Saudi regime obeys and fulfills them while trying to seek their own personal interest since they run a dictatorship.
It's the same with Syria, a war torn country that is still struggling with terrorism, separatism, US occupation, food and energy crisis has to try and get close to a hegemony and play their big geopolitical game. So they play in favor of Russia and in return Russia is providing aid to Syria to for example fight ISIS and US. Gives some air defense to defend against Israeli terrorist attacks such as the one today that hit two civilian airfields in Aleppo and Damascus. Helps rebuild the infrastructure US and its proxies destroyed. and so on.