How do i know my girlfriend and I are still worth being together?

We have been together for almost a year(4 days short). And she's been telling me lately that she misses the guy who made her fall in love, when ever i look at her tumblr or facebook its the same thing. She still tells me shes soooo deeply in love with me and I am too but i feel like i cant make her happy bcz..thats it i dont know why. I think its because she always tells me how sad she is when ever she is and doesn't tell me how happy she is when she is. I want to be with her so much but i dont know if i should leave her or not. She is the nicest girl i have ever met and i love her unconditionally but i just need help on what i can do to keep us together. She's on a tour across the U.S. for hula and she was'nt a loud to bring her phone so i see her on june 29th when she comes back. I really wanna hold this relationship down for the both of us