You obviously don't seem to know why you do a general election every 4 or 5 years instead of every year. The government can't implement everything they promise within such a short period of time. You wouldn't even notice what has changed and which party is responsible for it. Also the MPs would spend more time with campaigning than doing politics. A stable coalition government wouldn't be possible, since you're constantly fighting for votes.
Also this is still not a reason not do do another referendum. You just pointed at something different (a referendum is not an election after all) and then concluded that this must be true for this as well. By March 2019, the last referendum will be almost 3 years old. Also I hope you realize that the last referendum was only advisory at the time. Voting Leave or Remain didn't have any legal consequences
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.