Sorry to hear that Ray.
I'm not sure I can offer anything wrt the heartbreak. I don't recall ever doing much breaking up...I'm sure it'll happen eventually, but my not so extensive list of relationships either were either short & in high school, or they're still going.
If you're having a hard time accepting the end...then I would suggest taking some time to yourself, and away from O. Whenever I've seen people who try to go immediately from lovers to friends without any time to re-establish themselves as an individual, they never seem to break away from the couple mentality. Give you and him some space to mourn and rebuild.
As for friends...if you're breaking up on fairly amicable terms then it shouldn't be too hard to keep them around. Back home my social circle was fairly extensive and intertwined, with a few couples where both partners were closely tied to the group. When they broke up, it tended to cause a lot of strain all around if it wasn't peaceful, with lots of people taking sides, or getting torn between the two.
For the sake of your friendships, I'd suggest trying to make it easy for them to stay friends with both of you...however you can make that work. Hopefully O will do the same...it kinda sucks to be caught in the middle.