You already know what you need to do, so you need to just work up the courage and do it. Your parents will eventually understand, and you can always get another job when you get back. As for your girlfriend, I'll agree with some others that have said to see if she can come with you part of the time. If not, well, you need to work that out. No one here can give you relationship advice, but everyone here will tell you to travel if that's what you want to do. Good luck.

I want to take a long trip not a month , and I don't even have a month of free days left. And honestly I hate my job and wish to never do it again haha , so quitting my job is the right thing to do.
And I realize that I have to grow a pair and just tell em. I might piss my loved ones off but , it's my dream and I just want them to support me ( too bad they wouldn't support me :( )
Late night blatherings (it's after midnight here)
I just got of the phone with the ex-girlfriend about whom I have been posting.
We have been speaking several times a week since her divorce 2-3 years ago.
My love for her has never died.
Her love for me has never died.
Our journeys took us separate directions, and there is a sadness to that fact.
But if she had denied me the opportunity to travel, we would have had a different lifelong issue in our lives. Relationships are complicated.

Dude, your in your 20's, every time I took a long trip, my Girl fiend dumped my ars, every time, after a few trips I just got used to it.. If you want to travel do it, wait for friends and you won't travel much. Your Parent's will always love you.

It sounds to me like you already know what to do. You need to dump the girl and get on the road. She will, believe it or not, get over it and get on with her life.
You say you don't like hurting her, but what you're doing is being selfish. The quicker you tell her, the quicker she can get on without you. And the quicker you do, the quicker you can get on with your fun traveling plans without feeling guilty. Win-win.