Hi
We /my gf and i/ had broke up a long time ago
Now we are back on the track
We promised each other that we won't do the same mistake again
However I figured out that she still acts thoughtless, so I want to end it
But I'm afraid that I am not able to make it through when I do,
Because the first break was very painful, and I really don't know what to do... thanks

What does "thoughtless" mean?

If you really can't get beyond her "thoughtless" behavior, then just tell her. Just get it over with ASAP and move on. It'll hurt, but the sooner you do it, the faster you'll heal, and the faster you'll find that perfect gal.

Remember - ALL breakups are painful. There just isn't anything I can tell you that will make it pain-free.