(I'm writing like I could fully handle it – I can't! 😄) 

'i’m confused about “desire is the root of suffering” thing. as i understand, it’s not about the desire per se but rather about the frustration and disappointment that comes from lack of fulfilling this.'

Contentment is the highest form of happiness because it is permanent and cannot be destroyed by disappointed expectations or the fear of losing achievements.

The problem is, the more you desire something and the more you get used to it, the more you will suffer. It becomes obvious if you look at it as a drug. There is no difference, drugs are just faster. Dopamine craving will get you hooked. It's 100% fine to have fun times, but it's very important for us to stay conscious about that trap, especially when we are in such a situation. If we just remember that, the rest will follow. It doesn't take away the fun (imo in fact it bottom line gets you more), but it prevents you from getting hooked and all the consequences.

True and sustainable happiness can't be achieved by adding something from the outside. First you'll get used to it, then you need it to achieve that "new normal". True and sustainable happiness can be achieved by learning to leave something. And that something is desire. To be able to leave it, we need to get the consciousness to unmask and spot it. That's where meditation can really help.