As a general rule, you should never get back together with an ex. Like EVER. It almost never works out and tends to hurt twice as bad the second time.
That being said, you seem to suffer from WAY too much social inbreeding there. When you break up, the idea is to have separate social circles as much as possible. Dating friends of ex's is a huge no-no for all involved.
I agree on both accounts...to a degree.
Yes it's not usually a good idea to hook up again with an ex. I originally wasn't going to get together with her, and I told myself that for a while, I had my chance and I blew it. I did spiral out of control down to rock bottom, and from there I found my true friends.
Yeah, not a single one of the people that I called "friends" in real life gave a crap about me. Hell I vanished for a year without a word and not one of them even tried to come ask me what was wrong. And it was my first gf, I'M BOUND TO MAKE MISTAKES! Do I care? No. I'll be burned and learn. It's not like I'm completely in the know on dating.
Besides, we got a weird/awesome relationship. She pointed out my NES buying was a GOOD thing.