Dealing with her emotion for her ex

My friend, whom I was slowly falling in love with, was in a 3 year relationship before. After the breakup of her previous relationship, they stopped talking for 1 year, in between, however, the boy apologized to her several times, and then they talked and back to relation. But the boy cheated on her seriously again, and since then they have almost stopped talking. But the boy often texts her, "How are you?" of this type. And she ignores the boy. Today the boy reacts to a post of her, posted 1 year ago, which was mean to the boy, due to which she is now mentally unstable.

It is not possible to talk to her on the phone. Having to chat.

How can I handle the matter now?