<human>: Hi reddit, heres the story. Me [15M] and my [16F] now ex-girlfriend have been together since we started secondary school, so about three years and shes my best friend, like I cant go a day without talking to her or I just feel empty inside like somethings missing.

   Then out of nowhere she tells me that she wants to be single, and I obliged and asked if we could still be best friends and she said sure thing. So for about three months now weve stayed best friends but still in-love. 

But then she started talking to this guy [19M] and I told her that I didnt want her to do anything with him because it would hurt me. Guess what she did? She caught a ride with this guy at half one in the morning in his car (Which is very unusual for her she usually watches sex & the city and goes to sleep.) and they drove around and apparently made out. Which really tore me apart.

She keeps telling me that I can do the same to any other girl and she wont say a thing but I dont want that. It would feel wrong because it would be her and I love her and not some random girl.

She said she wants to do it again and I told her that I couldnt stick around if she did. The stress would literally kill me or give me a mental breakdown. Too much shit runs through my mind when she does stuff like that. She tells me she wants me to stay because im all she has and that she would be lonely. 

I know you might consider this juvenile Reddit but ive poured my heart out and I need some support..

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Girlfriend wants to be single but stay best friends. She breaks my heart and tells me she wants to do it again. I tell her I cant deal with the stress. Were stuck at a tie here and we need help.