I am to leave in vacation with my boyfriend for a week but I'm in a miserable state and it becomes worse as the time is passing by.

I have to move town next month and even though I try not to think about it, every time something goes wrong with my relationship I remember I have to leave.

I've been with my boyfriend for 9 months now and everything was perfect, literally perfect: no fights, no misunderstamdings, no mind games, no cheating, no disappointments... nothing. Though, at the moment is not going very well and the reason is me. I always feel like crying and I just cannot be happy. What triggers this state is the fact that everybody hates and avoids me for being in love with "a guy who doesn't deserve me" and even if I can go at his place, call any time and say anything to him I feel socially rejected and I feel like something essential is missing. I cry almost every night thinking that they might be right and I suffer for nothing. Useless to mention that nobody believes our relationship will survive at distance. I want to let time decide that but I don't want it to happen before I leave. The problem is that I don't feel like doing or saying anything so I am kind of a bore and even if he wants to spend time with me, he ends up joining conversations with other people and leaves me alone. If only I could be more talktive and get out of this state things would be so much different and we would live every moment at its best. But I can't. Even if I get in a better mood, he drags me back by acting carelessly or something embarrassing happens and I'm feeling completely left out by the entire world.

I want this holiday to be worth remembering but how can I switch my mood in such a short time? I don't want him to feel like trapped with a hipersensitive girl who should stay home and cry instead of travelling.

There's something not quite clear about this:
Things have been fine for 9 months.
But everyone you know disapproves of him (and you for loving him), leaving you socially isolated.
You tend to be depressed and quiet around him, so he ignores you.
You are moving soon.
You are afraid that long distance will ruin the relationship, and so do a lot of other people.
You and he are going on a vacation.

Whenever someone comes here and says that everything is wonderful and in the same breath says that a lot isn't right, I know there is confusion and a lot of communication lacking between the couple.

It's a cold reality that distance is a tough test of love, and many LDRs fail. It's also reality that we are social, and if you can't get people to accept the person you love, chances are you will be miserable. Add to that, you and your boyfriend don't talk about anything deep, I have a feeling.
So yes, it's bound to fail.

WAIT - how can you say that things have been so perfect? Reread your own post from a month ago! Why are you living in this state of denial? You haven't separated your own wishes and opinions from those of your family.
I have a feeling you are still very young. You never said how old.