This is the second question you have asked regarding this issue. Are you still hung up on this guy? Why do you even care about what he thinks? Are you dating his friend to get your ex's attention? Let your ex go. he left you remember? Move on. Do not play games. If you are playing games the validation you are looking for you are not going to get here.
No way. He's your ex for a reason. It's none of his business. He is the one that left you and it was a while ago. You don't owe him any explanation when it comes to your dating life. The two of you are done with.