What should I do about my girlfriend?

Me and my girlfriend are in a long distance relationship right now. And we were only dating 3 months before I had to go away, but we’ve been together for 8 months so far. And she has this friend that has been her friend for about 10 years, and usually her and her friend give eachother a peck on the lips now and then. But my girfriend told me this story that she kissed her friend. And I didn’t tell my girlfriend that it bugs me, because that was a real kiss you know? And then her friend got sent away recently for drug problems and now all my girlfriend talks about is how much she misses her friend and doesn’t so much as say a thing about her missing me even though I’ve been gone from her for months. I know my girlfriend is curious about other girls, she’s told me that now and then, but she said she didn’t want to be lesbian or anything like that. But this kiss her her missing her friend so much makes me thing she loves her friend more than me. And it hurts me because I love my girlfriend so much, and the fact she kissed kissed her friend hurts me more. What should I do? And should I feel this sad?