Getting frustrated day by day

I'm having a long distance relationship with a girl since 2011. Initially it was well and good, though we had issues. We talk mostly via FB. Few times i have found out that she has flirted with other guys in my absence. I was mad at her but then again I loved her truly so we were back together. Now the complication is, since november of last year i noticed a change in her. We dont talk regularly from then. No more long conversations. I thought she might need some space so I let her be on her own wondering everything would be ok very soon. Besides she had her exams during that time so I chose not to screw her up. But nothing worked, yes we did talk after that, but it was like once in two days. And one more thing I would like to mention is that, she was nomore interested in any romantic or intimate conversations. I tried to sort out by asking her. She said everything will be fine. She behaved reluctantly. Last month she had her finals in school and we had our anniversary after that. So I was quite sure she would be free and would be there online. I planned a lot of things to make it special for her, but she didnt come. I wondered if she is ok. And then I saw one of her guy friends uploading pictures of them together. I am a very possessive guy. After like 2 days, she came online, apologised that her phone (actually her mom's) was out of balance so she couldnt wish me that day. I asked her about the picture (not being hypered) and she said they had an ocassion on that very day in her house in which she invited that friend. I was heartbroken to find her behaving like I have no importance in her day to day life at all. Yes when she comes online, she spells i love u to me sometimes, but they feel like words to me now. I nomore find any hunger in her words for me. She never says she misses me but i miss her a hell lot. I wait for her everynight. And now..days have turned into weeks. I get her message once a week or may be once in 10 days. Is this a relationship or what? What does she want? What should I do? I am having a feeling that she might be cheating on me. Though I seriously do not want to be like those typical doubtful boyfriends, but situations and circumstances are forcing me to believe. I left a couple of emails in her mailbox complaining about what she's doing to me and wishing she would read them someday. I am getting frustrated. Am i over reacting? P.S: *my grandfather passed away last month. I informed her about that, but she didnt ask me even for once if i am ok. May be im expecting too much. *we were very happy with each other. We used to talk till late at night.Everything was perfect. She loved me alot. *we avoid talking over phone as she does not have her personal cell phone. *We stay in different countries. We haven't met yet as I am pursuing my studies here and it is not possible to travel to her country without my parents concern and I havent informed them about my affair till now.