I can offer some general insights into why a situation like this might occur. Keep in mind that relationships are complex, and individual experiences may vary.
Lingering emotions: Even after a breakup, there can be lingering feelings of hurt, anger, or resentment. It's possible that your ex was trying to be friends in the hope that those feelings would fade, but they might have found it difficult to move on while maintaining a close friendship.
New romantic interests: Sometimes, when one person starts dating someone new, it can change the dynamics of existing friendships. Your ex might have found it uncomfortable to continue the friendship if they or you started seeing other people.
Unresolved issues: Certain problems or conflicts from the past might not have been fully resolved during the friendship period. These unresolved issues could resurface and lead to negative feelings.
Different expectations: Each person may have different expectations and boundaries when transitioning from a romantic relationship to a friendship. If these expectations weren't adequately communicated or agreed upon, misunderstandings and conflicts could arise.
Changes in feelings: Over time, people change and evolve. It's possible that your ex's feelings towards you evolved, and they realized that they no longer wanted to maintain a friendship.
External influences: Outside factors, such as the opinions of friends or family, can influence someone's decisions and feelings about a friendship with an ex.
Personal growth: Sometimes, after a breakup, individuals may focus on personal growth and self-discovery. In this process, they might distance themselves from previous relationships, including friendships with ex-partners.
Mutual discomfort: Being friends with an ex can be challenging for both parties involved. Your ex might have decided that maintaining the friendship was causing them distress or preventing them from moving forward.
It's essential to remember that everyone's emotional journey is unique, and sometimes, despite the best intentions, friendships with ex-partners might not work out. If you're seeking closure or understanding, consider having an open and honest conversation with your ex, but respect their feelings and boundaries if they wish to keep their distance.