In the best of a bad business, you could have gone to him man-to-man beforehand and told him basically that he was being a cad, a scoundrel or some other noun of loathing and that he is using 2 other human beings for his own pleasure. That it's a low thing to do and that he would be causing hurt to 2 of *your* friends. That no real man treats a woman he cares about that way. You could try to bring some empathy into it: Would he like it if some woman played this game with him? That kind of thing.
Now he probably would have gotten mad and said things like it's his personal business (then why did he get you involved?) and that you're jealous (low blow) and so forth.
You could have told him that if he didn't do the right thing, that you would speak to one/both ladies. Or you could have said that your friendship is over and cut him out of your circle. It depends on him, you and how it went.
Ebor,
Thank you for your prayers as well as excellent suggestions.
In retrospect, I really could and most likely
should have gone about the situation in a different manner. I should have talked to him about it personally, but since I have been distancing myself from him, I haven't had any contact with him in almost a month and for me to come out of the woodwork only to tell him to clean up his act wouldn't have flown to be sure.
At the time I had told the other girl, my mind wasn't exactly clear as I had been up for about 19 hours straight and had had 2 hours sleep the night before. I didn't when I would talk to her again before he came, so in my mind at the time, it seemed like I was doing the right thing. It definitely isn't an excuse, more like a reminder to myself that when making important decisions like the one I made should be made with a clear and rested mind.
However, whatever comes of this will be at least one if not two womenfriends who will be hurt, confused likely and feeling betrayed because he *did* betray them.
I don't know if this helps any, sorry. It's a mess from any angle. But you didn't make it. He did. And telling him calmly but flat out that he was Wrong, might be a message he needs to hear.
Don't apologize, your words of wisdom have been most helpful.

If I come into contact with him again soon, I will be sure to tell him that I think what he was and has been doing is improper and also to point out that if the tables were turned, would he like it? I definitely think he needs to hear it.
Thank you again.
Prayer was said, but like most, how to respond was the question, maybe too much of a description was submitted.
Jakub,
People who know me would say that I talk way too much!

I posted the request for prayer on the night that I had spoken with her. At the time I posted, I had been up for 22 hours straight on 2 hours of sleep the night before.
Once again, there are certain things that should be done with a clear head.

I apologize for the overwhelming details.
In Christ,
Aaron