Why didn't Mueller recuse himself? He's been good friends with James Comey for 15 years and they refer to each other as 'brothers in arms'..... isn't that a serious conflict of interests?
No, it's not a conflict of interest if two people in a legal case are on the same side. For example, if a police officer has a long working relationship with a prosecutor, that's not a conflict of interest for a police officer to testify in that prosecutor's case. It would only be a conflict of interest if the prosecutor was charging the police officer with a crime.
Comey is essentially a witness for the prosecution, not someone under investigation, so he's on the same side as Mueller, so it's not a conflict of interest.