I need some advice please help. (short and easy question).?

Well i have a girlfriend that I love very much. We've been dating for about 9 months now. About a month ago she left for a 2 month trip to puerto rico. So she has about a month left before she comes back. The other day we talked on the phone, she said something like "we will probably just end up being friends, that happens a lot to me". I told her we wouldn't but she insisted. I told her I didn't like hearing stuff like that, but it didn't matter. We were really close before she left but now...idk. What should I do or say to her? This is making me sort of depressed, and making me want to do nothing but lay in bed all day...