In the end, its totally up to you to decide what the best move is. If you think it would be less upsetting for them to hear it from you, or if youre sure that youve both moved on and just want to let them know whats going on in your life as you would with any other close friend, then go for it.
If so, you need to let them know youve been in touch, and that its not a big deal. Honesty and communication are essential to a healthy relationship, so if you and your current partner always tell each other everything, then they might feel a violation of trust if you dont tell them your ex texted you.
Should you tell your ex youre talking to someone?
You dont have any obligation to tell them. This is especially true if it ended badly, there are still hard feelings on either side, or one or both of you did not take it well. Sometimes its better to set a boundary and not have any contact.
Should I respond to my ex if Im in a relationship?
It is definitely OK not to respond to ex. In fact, in many circumstances, you might find that you shouldnt text back. Receiving a text message from an ex can sometimes be a good thing, perhaps even more so if you ended on good terms and are open to rekindling a relationship.