What is when a guy friend starts acting different?

When a guy friend starts acting different, it could be an indication that something is going on in his life. Here are some possible reasons:

1. He might be going through personal problems such as family issues, emotional or mental health problems.

2. He may have started dating someone and wants to focus on the relationship.

3. He might be struggling with work or school-related stress.

4. He may have changed his interests or priorities and has new hobbies or friends.

5. He may be jealous or resentful of something that happened between you two.

6. He may be feeling distant because of a misunderstanding between you two.

It's important to communicate with your friend and try to address the source of the change. However, it's also important to respect his boundaries and give him space if that's what he needs.