Just because you have moved past your ex does not mean that your relationship history and the feelings that go along with it have gone away. While some exes are able to move on quickly and care little about whether you are dating someone new, other exes may have strong feelings about you and your new partner. The reasons your ex may care depends on the nature of your relationship as well as other factors, such as his personality and past experiences.

Hopes of Reunion

One reason your ex may care if you are dating is because he still holds onto feelings for you. This may be particularly true if you were the one to end the relationship. If your ex tries to stay in regular contact, has tried to reconcile with you of if you have broken up and gotten back together before, there may be a chance that he has been holding onto hope that you will get back together with him. In this case, he may be feeling hurt, jealous or sad about you dating.

Unresolved Emotions

Although you and your ex may have mutually decided to part ways—or indeed, even if your ex was the one to decide to split up with you—this does not mean that she no longer has feelings for you. Because it can take months or even years to recover from a breakup, she may have not had the chance to process all of her feelings toward you, says licensed social worker David Braucher in the Psychology Today article “Why Can’t I Get Over My Ex?” Although she may not be interested in getting back together, the thought of you with someone else may evoke jealousy, anger or remorse.

Jealous Personality

If your ex was controlling, he may be upset about you dating again simply because he does not want you to be with anyone else. This may be what is going on if your ex tried to control you when you were together—for example, if he tried to limit your time with friends and family or became angry if you talked to male friends. Since these can be the signs of an abusive dynamic, minimizing contact with a controlling ex may be the best option for both you and your new dating partner, according to the article "Domestic Violence and Abuse" from the nonprofit HelpGuide.

Friendly Concerns

If you maintain a friendship with your ex, she may be concerned about your new choice of dating partners. These concerns may not be motivated by jealousy but by sincere worries that you are dating someone who is not a good fit for you or is not treating you with respect. If she has talked about her worries in terms of whether you seem happy and content, it may be worth listening to your ex and considering whether her feelings are valid and based on friendly concern and thus, something to keep in mind as you proceed in your new relationship.