Girlfriend and ex trouble?

Need advice on my girlfriend. I feel like she always puts her friends first than me. I sent her these chocolates and flowers for our monthsary and she didn't even say thank you. Meanwhile, I have an ex who says she wants me back. She kept on adding me on Facebook and sending me letters. My ex was the one who broke up with me and left me broken hearted until I found my girlfriend. One night my girlfriend was staying up late partying with her friends and I found myself thinking of my ex. I don't want to think of her, but then I began appreciating that she gives me attention today and the effort she puts up. But I'm not in love with my ex anymore. I'm in love with my now girlfriend but I wish she can show more dedication to our relationship like the desire my ex is showing me today. What can I do? And why are girls like that? You show her love, she dosent appreciate you and treats you like ****, but when you're no longer in love with her, she wants you....????