It can be difficult and painful to find out that an ex-partner has started a new relationship. It can bring up a range of emotions, including sadness, jealousy, and even feelings of rejection. It's important to remember that it's natural to feel these emotions and to allow yourself to experience and process them. It can also be helpful to remind yourself that nobody is indispensable and that it is possible to find happiness and move on from a past relationship. It may be helpful to talk to a trusted friend or family member, or even seek professional support to help you through this difficult time.