My girlfriend dumped me by text message and I'm depressed?

So my girlfriend and I went out with some of our friends to a nightclub cause that's what we usually do on Saturdays. Well the night started off well, I really didn't see anything wrong. She didn't want to dance just one on one but that's how she is so I didn't see anything abnormal. Then she started disappearing for lengths of time, always coming back but I didn't really think anything of it. She just didn't give me much attention throughout the night whatsoever. So then the downstairs punk stuff finished and we went upstairs, and our other friends went home and she wanted to stay so I stayed with her. Noticed she was grinding up against a few other guys, but I thought she was still drunk so I didn't think anything of it. She told me that I looked like I just wanted to go home, I was kinda slowing down cause the music was that kind of electro dance and it wasn't my thing. I had to get my backpack from cloaking cause they closed, and so I left the dance floor to find somewhere to put it and I grabbed some water. Then I feel a vibration in my pocket, open my phone and it simply read "I can't do this anymore I'm sorry. Your too young for me" (I'm 18 she's 22) and without saying a word or even looking I just left the place, found a taxi and went home, didn't say a word but inside I was screaming. It was just so out of the blue, didn't even see it coming. I genuinely had feelings for her and now I feel used. We were dating for two weeks, and I was starting to fall for her and then all of a sudden this. Now it's the day after and I have no motivation to do anything, I've been laying in bed all day. How can I get over her? It was pretty much attraction from the moment I saw her, and it just kills me inside because I feel like she used me and just got bored