It's challenging to determine the exact reason without more context, but there could be a few possible explanations for your ex taking credit for you meeting your new boyfriend:
Ego and Insecurity: Your ex might be feeling insecure about the breakup and wants to maintain a sense of importance or control in your life. By taking credit for you meeting someone new, they may be attempting to make themselves feel better or trying to assert that they still have some influence over your happiness.
Seeking Attention: Your ex might be seeking attention or validation from others by claiming credit for your new relationship. By doing so, they might be hoping to gain sympathy or admiration from mutual friends or acquaintances.
Regret or Jealousy: If your ex still has feelings for you or regrets the breakup, they might be trying to cause jealousy or stir up emotions by inserting themselves into your new relationship. It could be a way to elicit a reaction from you or see if you still have feelings for them.
Misinterpretation: It's also possible that your ex is misunderstanding the situation. They might genuinely believe that their actions or influence led to you meeting your new boyfriend, even if it's not entirely accurate.
Regardless of the reason, it's essential to stay true to your own feelings and not let your ex's claims affect your new relationship. If your ex's behavior becomes problematic or causes discomfort, it might be best to establish clear boundaries and limit contact with them. Focus on nurturing your current relationship and prioritize your own happiness and well-being. Communication with your new boyfriend about the situation can also be helpful to ensure both of you are on the same page and can navigate any potential challenges together.