When a man is involved with a lot of female friends it can also be a warning sign that he is not a man who is ready for a relationship. I know many men who have a ton of female friends who havent been in a committed relationship in years or ever.

Is it a red flag if a guy doesnt have a lot of friends?

Having a guy who has no guy friends often can indicate that he doesnt have any real friends at all and thats usually a bold red flag.

Should I be worried if he has a girl best friend?

Even if one or both of the friends are involved in a relationship, this need not be a concern. As Manly explains, in a relationship, if both partners feel safe, secure, and bonded the sex of the best friend is a non-issue.