There could be several reasons why your ex repeatedly praises his new girlfriend when speaking to you, even if you never respond:
Trying to evoke a reaction: Your ex may be seeking a reaction from you, whether it's positive or negative. He might want to see if you still have feelings for him or if you are affected by the fact that he has moved on with someone else.
Jealousy and comparison: By praising his new girlfriend, he might be trying to make you feel jealous or insecure about yourself. He could be attempting to highlight how great his new relationship is compared to what you had together.
Boosting his ego: Complimenting his new girlfriend in front of you may be a way for him to boost his own self-esteem and feel more confident in his new relationship.
Demonstrating happiness: It's possible that he wants to showcase how happy he is in his new relationship and wants you to know that he has moved on and is doing well without you.
Seeking validation: Praising his new girlfriend when speaking to you could be a way for him to seek validation and approval, especially if the breakup was difficult for him and he wants to prove that he made the right decision.
Manipulation or control: In some cases, this behavior could be manipulative. He might be trying to control your emotions or keep you invested in his life, even after the breakup.
Regardless of the reasons behind his behavior, it's essential for you to prioritize your own well-being and emotional health. If his actions are causing you distress or discomfort, consider setting boundaries and limiting or cutting off contact with him. It's important to focus on your own healing and moving forward, rather than dwelling on his actions or trying to decipher his intentions. Surround yourself with supportive friends and family, and consider seeking professional help, such as counseling or therapy, to help you process your feelings and emotions after the breakup.