I don't think I would go away with an ex, especially not if I was dating someone else. Unless, I was very good friends with this person for a long time before we even started dating and if our friendship had still been continued.
It's weird if you ask me. I don't know what advice to give you.
To love is to suffer. To avoid suffering, one must not love; but then one suffers from not loving. Therefore, to love is to suffer, not to love is to suffer, to suffer is to suffer. To be happy is to love; to be happy then is to suffer, but suffering makes one unhappy; therefore to be unhappy one must love or love to suffer or suffer from too much happiness. I hope you're getting this down.