You are helping an ex on something when she starts talking about her miserable love life to you. Somehow, you say something that triggers both of you to talk about your past love. Something like "Thats what you got cos you didn't chose me." The talk from helping her changed to discussing about your past love with her, the reason why she broke up with you, etc. Your girlfriend is on WhatsApp chat with you at the same time and you reply her once in a while only cos you are being occupied with your ex. You also encourage your gf to do whatever she is doing eventhough she says she is free.
Does that consider as cheating?