I have had an abscess just above my bum and it burst the other day, pain has subsided and bleeding is far less, though there is still some serous flui?

Pilonidal cyst: It's probably a pilonidal cyst, and needs to be definitively removed. Usually a surgeon does a small procedure to remove it but they can recur. Bc they can be deep, it's best to have this done in the operating room... Since it burst, this could be after the initial inflammation has subsided a bit. Give your doctor a call or look for a general surgeon/colo-rectal surgeon. Warm soaks for now.

What's the question?: Well, that's one way to handle an abscess - wait for it to burst. The healing process should begin now that the space containing the infection has been emptied of its contents. But you didn't have to go through all that pain and (probably) worry -- if it ever happens again, get to a doctor early in the course and get it treated in a less painful and more civilized manner.