It's almost incredible how you sound like I would a few weeks ago
See, I've been at this exact point, with the exact same symptoms. I'll tell you what I did, so you don't let it happen to you:
In 2012, I went to Spain for four months. After coming back (and sort of experiencing the single life, if you know what I mean), it wasn't the same. Also, what added up to the bad experience after coming home was that my gf at the time had to do a fairly terrible placement at the time. During this time, I was the one initiating everything. When I started uni a few months later, I had already realised I didn't want to be with this girl anymore. But I kept myself from doing the right thing and breaking up with her, probably because of the convenience you mentioned. Also, she was a very good friend for me and some part of me did not want her to get hurt by a breakup.
Long story short, We broke up during semester break. But believe me, the last weeks/months were terrible, and it makes you feel bad about yourself too, which I only realised AFTER breaking up. You know, relationships are not pointless, but at your stage in life (and mine, I'm turning 20 soon), settling down might not be what we're after. I don't think living the life of PUAs is your motivation; you don't love her anymore and you're making up the very same lame excuses I did.
I reckon you have trouble telling her that you simply lost interest. Ask her to meet you somewhere, and go to a bar or cafe, make sure it's not too crowded or a place you would go normally, you don't want people to recognise you and interrupt the breakup. Tell her that the relationship right now isn't right for you anymore. Most basically, you're doing the 'it's not you, it's me'-line. But make it personal and honest.
About being friends after breaking up: I'd recommend that you don't initiate contact. Like me, you won't be the one having trouble getting over it, but she will. Respect that and give her space, if she texts you, reply in a polite or otherwise appropriate manner. But don't initiate contact. She might text you weird things, or memories from your relationship; ignore that. It will be tough, but you will feel better about yourself after.