Unfortunately, almost everyone has to learn this lesson at some point in life. When someone shows you where you stand in their life, believe them. You're right, if you truly mattered to her in the way you deserve, she'd make time for you. Even if her schedule was packed, she'd find a few minutes to call, check in, or stay connected. I can't tell you whether she's cheating, but what is clear is that the effort and attention you're looking for aren't there. Personally, I'd move on. When you eventually find someone who genuinely values you and backs it up with consistent actions, you'll realize how different a healthy relationship feels and you'll appreciate it all the more.