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.
What to do when you find out your ex is seeing someone else?
How To Deal If Youre Having A Hard TimeLet yourself feel whatever youre feeling.But refrain from acting on those emotions.Stop looking up your ex and their new S.O. on social media.Figure out what excites you.Come up with your own “letting go” ritual.Consider seeing a therapist.15 Jan 2020
Does seeing your ex with someone else hurt?
It may just be your ego getting bruised. “Ego can play a big role in feeling hurt,” Davis says. It makes them feel wanted.” Theres comfort in thinking theres someone out there whos still hung up on you.
The person who did the dumping usually feels strength (and often relief) at the very first, but with the days and weeks of no contact your ex likely begins to develop feelings of doubt in their decision, missing you, fear that you have moved on, and confusion that you have not chased, begged, and pleaded as most others