Yeah, everyone here is pretty much saying to tell her, I agree.

Even if she says 'no' she'll still be aware of your feelings and if she does have any feelings for you (although maybe not enough at this time to break up with the guy), you'll still be around when this other guy goes off travelling and it'll give you two the chance to get to know each other 'better'. And those feelings she has for you, no matter how small, may always grow...

You have to get it out your system, deal with whatever she throws back at you, and, if required, get over her and move on... it's easy to get obsessed with someone (especially when it's someone who isn't so easy to get) but you must realise there is so much more out there and as soon as you find someone who fits, all the pain you have right now will quickly fade.

It will, even if you don't think that's possible right now.

But tell her now.