Responding to an ex's message is a complex topic. Some online relationship counseling experts recommend replying politely to avoid pushing them away. However, our experience indicates that responding to trivial messages or provocations when you want to get your ex back can actually drive them further away, as it suggests you're still in a weak position. An additional drawback of responding is that it causes you to ponder over how to reply, and the more you think about your ex, the higher their subjective value becomes in your eyes. This increases your anxiety and slows down the recovery process.
Typically, when you respond, the conversation gradually fades away, and they lose interest
or abruptly stop messaging you right after receiving a response. Even in cases where it appeared they wanted something from you, the moment you respond, their need vanishes.
Ultimately, the decision is yours. If you believe that answering a casual "how are you" after being cheated on will help win them back, go for it.