I'm thinking the problem is, that she starts to doubt the relationship, forget that things are good and fine, w/e while you two are apart. But when she see's you she remembers, which would be why she acts like things are alright. Maybe she just doesn't like the distance? (speaking from experience, btw) Being apart makes things really hard on a relationship, but if you both want it to work it SHOULD work.
And I'm confused on if you two are still DATING or no?
(And if I don't reply it's 'cause I'm going to watch movies with my Mom.

But I'll be back soooon)