a. It's important to address the situation in a calm and professional manner. You can schedule a private meeting with your boss to discuss the situation and try to understand why they are taking your co-worker's side. You can also try to have a conversation with your co-worker to understand why they are speaking negatively about you and try to resolve any misunderstandings. It's important to remain calm and professional throughout the conversation and avoid getting defensive or emotional.
b. Avoiding the co-worker and your boss may not be the best approach to resolving the conflict. While it's important to take some time to process your emotions, avoiding the situation entirely can make things worse. Instead, try to address the situation directly by scheduling a private meeting with your boss or having a conversation with your co-worker. This will show that you are taking the situation seriously and are willing to work towards a resolution.