Hello I know you posted this one month ago but I am still going to answer it :D.

The reason why romanian is a romance language and why did it not get slavicised is subject of debate amongst scholars, it is certain though that it isn't a modern invention.

Most scholars consider that one of the main reasons why latinity endured is because of the people's pastoral life style, sheep herding is considered one of the country's oldest profesions and it was no diference during antiquity, in fact the romanian word "baci" meaning shepherd is one of the few dacian words left in the romanian lexicon sugesting clearly just how old and important this profesion was. These men used to and still live isolated lives in the Carpathian mountains, after the roman administration retreated, these people endured in mountain villages while the lowlands where overrun by migrating peoples, amongst these people those that where most proeminent where the slavs, now slavs where farmers with little interst in moving to ruged mountains, why put an aditional effort to moving sonewhere you are not used to when there is easily accesible countryside to farm.

At some point during the dark ages, the latinised populations which had waited out the ravaging invasions of migrating peoples descended from the mountains and subjugated the slavs, slavs where majoritary but probably not by a large margin because latin elements prevailed in the ensuing fusion between the two languages, modern romanian language has 70% latin elements and and about 20% slavic influences.

As for why Romania is Francophile, at the begining of the XVII'th century, romanians started to realise the latin heritage which they had ignored, scholats compared elements of the basic vocabulary (the fundamental building blocks of any language) and found clear similarities with other romance languages, not only that, but in certain aspects, romanian was more latin than these languages, the basic verb "to be" is a good example of that. During the rise of national awareness during the XIX'th century the latin pedigree was promoted as a means of uniting the romanians and as a reason to asociate themselves with western cultural patrons.

France was chosen as patron for multiple reasons:

France was a prestigious nation with a long and glorious history and a powerfull empire, in comparison to the non-existent Italian state and the bankrupt Spanish and Portuguese Empires.

French language was fashionable all across Europe, elites spoke it as casualy as we speak english today, if you read War and Peace by Tolstoi, you will see the russian nobles speaking entire paragraphs in French, this was the reality of the time, so adopting French language and culture was a means of asociating with western civilisation.

France was also a latin country so romanians looked to it as a big brother and example for what the romanians should strive towards.

After the Crimean War, the French suported the romanian initiative of unification of the two Danubian Principalities into the United Principalities the origin of the modern romanian state so romanians partialy owe their existance to them. After the Independence War of 1877-1878 which saw the creation of the Kingdom of Romania, france was amongst the first to recognise romanian independence.

Many other instances when the French helped us such as the Berthelot Mission in WW1 or French investments in the romanian oil fields and industry.