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.
In the first place, How would you know that he is a scammer? Because in that situation, it turns out that you are a scammer, you're making a deal with someone who even sends you first. It is never an excuse if it is the time of your presentation, for sure there is a time for you to reply to him and make him aware of your situation.
It was a big mistake to trust strangers but if you are not really a scammer, you will send back his money and clear your reputation. Feel your conscience and do what is the best thing to do, for sure you know it and to prove that you are not a scammer.