I think your friend has some good advice for you... I have a very very close friend that is a RA and she was so helpful in explaining things to me when the true reality of my situation started coming to light.. Sometimes it's easier to see things when someone from the other side starts telling us the cold hard truth about addiction.
Sweetie, I don't think any of us had any idea how complicated addiction could be until we found ourselves stuck in the middle of things... then we did what our human nature told us to do and we tried to fix things and of course we now all know that we can't fix something when we didn't cause the problem in the first place..
You are in a painful place right now but I can tell you as time moves forward and you begin to heal that your pain will turn to joy.
Now that your ex is out of town for awhile, start putting some boundaries in place for yourself so that when he gets back home and comes crawling back to you (and he will) you will be strong enough to say NO.
Also try to find some meetings in your area and start attending as many as you can.. Meetings will give you the tools to start your healing process..
Remember One Day at A Time