Guild Wars 2

Is this purchasable or free expansion. (if purchased how to purchase?)
Will new zones and class be unlocked for only those with expansion?
Will masteries be respeccable?
Will my gf dump me after I spend all my time leveling characters #25-28 and maxing their masteries instead of with her?

It’s a boxed expansion for which you’ll have to pay. That’s all we know atm.
You’ll have to wait for more info, just like the rest of us.

Here are 2 links that will help you answer your questions.

https://heartofthorns.guildwars2.com/en/?_ga=1.220096028.442872161.1420652610

https://help.guildwars2.com/home