So if we'd have voted to remain, it would have only been advisory ? We should have had another vote nearly 3 years later? And every three years then on?
Of course it would have been advisory. You were already in it, so it wouldn't have changed a thing. However the government (with the help of the parliament) could've easily ignored the remain vote and still initiate the Brexit as it is today.
There's no reason to make that final decision almost 3 years before the change begins. If you still vote with leave, then no. You will leave, immediately. No 3 more years since that was the necessary contractual amount to wait to declare the Brexit (well 2 years AFAIR but the UK government wasted a few months). However as I mentioned before, referendums do return. There is no decision that will decide your fate for all eternity. If there's demand for it, there could be another referendum to join the EU again within the next 5 years....if the EU agrees to that of course.