Cheating

I honestly don't understand what I do wrong in relationships. I'm 17 and I treat guys like gold. My last 3 relationships I have gotten cheated on like its no big deal. I'm one of those girlfriends that will buy you anything, help you do anything you need and support you 110%. My last boyfriend cheated on me after I bought him 250 dollar tickets to see Jason Aldean. During the concert he was texting his new girlfriend and I had no clue. He was singing to me and telling me how perfect I was then the next day he told me he was cheating. Is there any ideas on what I could do different in my next relationship? Or is this just how most guys are?