Coincidentally she cheated on me and ended up pursuing a relationship with the person she cheated on me with, ultimately, resulting in heart break.

She came back with her tail between her legs and went on about how foolish she was, etc. but it was already too late.

Sooner or later people will realize they made a mistake and let something amazing go, and naturally, they want to recover it. Add the fact that you are attractive and it probably burns them up even more, knowing that they had all that, and now they have nothing. So they continue to press, hoping to recover something that once was.

The best thing for you to do is ignore them. Don't even open their messages as they will see you saw it, and continue to harass you out of sheer thirst or hope.