I have so much heartache

[Its alittle long but please help, thank you] Ok so it started out I get a message from my girlfriend (she lives in a different state) and she asked me if I was hiding something from her. I don’t hide anything from her, I love to tell her everything thats going on with me so I asked what she meant and she started accusing me of cheating on her. I found out later she looked through my pics and found a tagged pic of me and my friend Jennifer. So my girlfriend automatically assumed I was cheating on her??? She said because we were sitting on a bed and that Jennifer had shorts on and it looked like we just got done having sex???! I don’t know why she would even think something like that, my girlfriend means everything to me and she always has and without her I would be absolutely nothing. She’s not just my girlfriend but she’s my best friend and we both gave each other our virginity. I love her with all of my heart and it hurt so terribly for her to accuse me of cheating without any evidence of anything at all and not believing me when I said nothing was going on. And then I found out that on her assumption that I was cheating (before she even talked to me about it) she had been crying and she had told my best friends that I was cheating on her thus turning everyone I know against me, so now everyone hates me and wont talk to me so I can tell them whats really going on. I have so much heartache and its making me sick over it =( . Please help me, what am I supposed to do?