She has a boyfriend...

• I've known her since we were 6 years old. We went to all the same schools together. We're both 21 now in the same university.
• This girl used to like me a lot and I liked her back, but I was too scared to do anything
• Eventually we drifted apart in university and she got a boyfriend (they've been together for 2.5 years)
• I'll be going away to another university 1000km away in a months time

Should I tell her how I've felt for so long? I know it's probably not the best thing to do but I can't stand keeping all these feelings inside. Especially when I know I'll probably never see her again.

I had a class with her last year and we sat next to each other every time (since we didn't know anyone else in the class). It seemed like she showed very small hints of interest, but that may just be me reading into it too much.
I've been talking to her on Facebook recently, just talking about the general stuff like what we've been up to and what we're going to do in 2015 and what jobs we want in future. When I asked her what she was up to for Christmas and new years (if she was going back to visit our hometown or not), she never replied (why?).
A month later I messaged her again. It's sort of like mindless conversation, asking how her studentship is going and stuff. I suggested we should hang out sometime before I leave, and she said we could go get lunch together or something. Would this be a good time to tell her? Would it catch her off-guard?

I don't know what to expect to get out of telling her how I feel, but at least I'll get it off my chest. Any thoughts on this would be nice.