I know that when you're trying to work through something like leaving someone behind or making a choice between travelling and someone who means a lot to you, answers like "It will work out if it's meant to" can seem glib, cliched and even unhelpful.
But really that is what it boils down to. If there is love at the heart of any relationship then the other person will want you to fulfill your dreams. They will want you to be happy, they will let you go and they will wait for you. And if you love them you will come back to them.
Other than knowing that fact, there is no point worrying about it. If the desire to travel is really strong, then you have to look at how important that is in comparison to the person you are with right now. I can't relate to be honest, because I have never had to make the choice. However, I am a big believer in true love. If the other person is clipping your wings, or wont let you be yourself, then do you really want to be with them?
If anything, doing something like going travelling without them for a while is a great way to test the strength of your relationship. It's a good way to test the level of trust between you.
And if your worst fears are realised and you do find that you outgrow that person because of your travels, well, even then, you'll still be happier because you'll know then that you made the right decision. On the flip side, if you leave and you can't bear to be without them, then you'll give up your travels for them because they mean more to you.
So, by making the choice to travel you will find your answer I think.