Yes, the first life was produced from a protein 'soup' so rather than one single organism, it was more like a coalition of chemical elements which created life as a combined effort. This stayed that way for millions of years until a mistake (mutation) was made with this life's re-creation and evolution was born.
You need to understand that evolution is not a straightforward event. Many creatures can not cope with the forever changing climate on Earth, most changes are not beneficial to an animal so are lost as that animals will not be as successful as others od it's own species.
So yes, we were all once primitive microscopic pond life. The first mammals evolved over 250 million years ago and stayed pretty small as the planet was ruled by gigantic reptiles. The mammals survived the extinction of most of the dinosaurs and rapidly evolved into a large range of animals.
We started separating from our apelike ancestors about 5-6 millions years ago. Men is the latest species that evolved among the mammals. Our closest ancestor was Neanderthal Man which is said to be extinct, but similar DNA has been found in some regions of Europe, so promiscuity is not new.