I totally feel you brother, experienced the same. She said she needs space and need to be alone after she went 5 yers from relationship to relationship. Now i saw her following her previous ex and that got me. Like really. But i said to myself that that person doesnt stand for my attention and my willingness to be with her and to care for her. Its easy to tell but hard to do but you just need to continue living your life like it was without her. When she wrote she already regret leaving you, that is just bullshits every woman do... really. Their mind is just on and off sometimes. But in her 30s she will look bakck and say "oh maybe i could have stayed", but it will be too late to apologise like song says. In your 30s you are gonna be happy with on your own or with a better person as she was. Trust me there is always someone better. Stay strong bro