I have one question am I a scammer too or did I do wrong by not sending him his Etherume back because after this incident my conscience has been beating me.
stay safe.
Yes, you are the other guy must have a good motive when sending you he just wants to trade unless you have a proof that he is indeed a scammer by reading one bad report about him, in the first place if you think the guy is a scammer you should not entertain him.
Free yourself by refunding him you don't want to get tagged as a scammer, this guy has a reason to create a bad report about you for running away with his money, and your suspicion is not justified to scam him.