I can offer some general possibilities for why your ex might still be angry and cold towards you six months after the breakup:
Lingering emotions: It's possible that your ex is still dealing with strong emotions related to the breakup, such as hurt, betrayal, or disappointment. These feelings can take time to heal, and some people may need more time than others to process their emotions.
Unresolved issues: If there were unresolved issues or conflicts during the relationship or at the time of the breakup, your ex might still be holding onto these feelings. Lack of closure or communication can contribute to ongoing resentment.
Coping mechanisms: Everyone copes with breakups differently. Some individuals may cope by distancing themselves and putting up emotional walls to protect themselves from further hurt.
External factors: Other life events or stressors might be influencing your ex's behavior. Difficulties in their personal or professional life could be affecting their mood and how they interact with others.
Jealousy or regret: Your ex might feel jealous or regretful about the breakup, leading to anger or coldness as a way to mask their true emotions.
Misunderstandings: It's possible that there are misunderstandings or miscommunications between you two, leading to tension and negative feelings.
Not ready to move on: Your ex might still be processing the end of the relationship and isn't ready to move on or be friends yet.
Regardless of the reasons, it's essential to respect your ex's feelings and give them the space they need to process their emotions. Trying to force a resolution or pushing for a friendship may not be helpful if they need more time to heal. If you want to improve your relationship with your ex, consider having an open and honest conversation to understand their perspective and feelings. However, if your ex remains unwilling to engage, it might be best to focus on your own healing and well-being.