Option 1

Arrange a private meeting with your colleague to address the issue directly, emphasizing the project's importance and the need for professional collaboration despite personal feelings.

Option 2

Report your colleague's behavior and their refusal to apologize to your project manager or HR department, requesting their intervention to resolve the conflict or reassign project responsibilities.

Option 3

Avoid your colleague as much as possible, communicating only through email or project management software, hoping the tension will eventually subside on its own.