I'm best friends with my kid's mother. We got together in high school, reproduced, and tried to make it work for several years. We were together 6yrs, and this is going on the 11th year since we first met. I wasn't an easy break-up (though had we been more mature and honest it should have been), we both truly loved each and wanted to make it work for the kid. At one point, we both agreed we were "soulmates", however we were too like-minded. We both needed an opposite for balance.
At first, there was some hurt feelings. Then we got over it, realizing we both liked the same shit and had the most fun together. We tried fucking, but feelings kept fuking with our friendship. Now we are the best of friends, we turn to each other first when seeking advice. We kick it all the time, and I've become great friends with her current boyfriend. It is a lot of work though.
As to Animal Mother: In our case, we DO still love each other and want to be close...just not on a sexual level. We have been a whole slew of fucked-up statuses; together, in an open-relationship, seperated but roomies and friends, enemies, friends w/ benefits, and best friends. If not for our kid, I wish we could have skipped all the BS and went straight to here, though we prolly wouldn't be as close. Sex just complicated shit. It's mutually understood that we are looking for different people, and fucking just makes us wanna be together, something we suck at. Instead, what we have is something special; a best friend of opposite gender, with whom we have no secrets, who can give unbiased advice. Though, in concession, we do have a kid, and both of us believe we HAVE TO interact civilly, and therefore might as well make the most of it. We were fucked-up kids and hurt each pretty bad in the past. Without a common link, we prolly would have hated each a lot longer, and whilst most likely still being acquaintances (living in the same small town with a small user population), we would have had no incentive to cast away the stone.