I love her so much but i lost her.....?

I been with my girlfriend for a year but since last Feb. I had to go to work a few hours away from her. I wont be able to see her until this September. I love her to death she tells me the same thing but just yesterday out of the blue she told me she just wants to be friends. Which crushed me really badly. I asked her if i did anything wrong she said no that im perfect and that she loves me but she cant take the stress of not seeing me. But i learned today she has been talking to three different guys having i guess you can call it online sex lol. sending pictures to them. she told me everything is all right. I mean i did everything for her i helped her when she needed it i did everything. But now she is gone it really hurts. i mean she doesnt know that i know all this and i havent talked to her since yesterday morning. What do i do? Should just throw away all our pictures and stuff together and just move on? What if she calls me or texts me do i answer them? I mean im a wreak right now and being a nice bguy sucks cuz all we do is get hurt and cheated on.Everyone tells me i am a good guy and that i donothing wrong but with this just happening to me i feel like i am doing something wrong like im a bad person and that i should of been there more :'(