When your ex kept repeating "That's nice" after you told him about meeting a new man and liking him, there could be several reasons for his response:
Indifference: He might genuinely be indifferent to the news and not have strong feelings about your new relationship or your feelings towards the new man.
Politeness or Awkwardness: "That's nice" can be a generic response that people use when they don't know how else to react in a situation. It could be his way of being polite or trying to avoid any awkwardness.
Hiding His Emotions: Your ex might have mixed emotions about your new relationship but chooses not to show it. "That's nice" could be a neutral response to conceal any feelings of hurt, jealousy, or discomfort.
Feeling Uncomfortable: Hearing about your new relationship might make him feel uncomfortable or awkward, especially if he hasn't fully moved on from your past relationship.
Avoiding Drama: He may not want to get involved in any potential drama or conflict and, therefore, responds with a neutral statement to keep things low-key.
Respect for Boundaries: He might be trying to respect your boundaries and not overstep by expressing strong emotions about your new relationship.
It's important to note that interpreting one phrase or response can be challenging without more context and understanding of your ex's personality and emotions. If you are concerned about his reaction or your interaction with him, consider having an open and honest conversation about your feelings and intentions moving forward. Communication can help bring clarity to the situation and allow both of you to navigate the post-breakup dynamic in a healthier way.