The referendum was not advisory. DC said it was a once in a life time opportunity and that regardless of the result he would ensure that it was implemented; then of course when he didn't get the result he wanted he resigned. (Fri 16-Aug-19 11:30:46)
The longer people continue not to understand the difference between the law and politics the longer they will feel upset.
Legally and democratically the referendum was advisory. When Parliament passes a bill such as the European Union Referendum Act 2015 it would have to declare, in that bill, if it was giving its executive powers (powers to make a decision) over to anyone else. In this case the voters.
On 3 November 2016, the High Court in London ruled that it is the responsibility of Parliament (and not of the Government unilaterally) to decide whether, when, and how the UK should set aside legislation (in this case, the European Communities Act 1972 that makes the UK a member of the EU). The court held that the referendum was "advisory for the lawmakers in Parliament", enabling the electorate to influence Parliament in its policy decisions. In interpreting the intent of the Act, the court considered the precedents of previous UK referendums. As a consequence, the European Union (Notification of Withdrawal) Bill 2017 was introduced into Parliament to gain Parliament's consent for the invocation of Article 50. (wikipedia.org).
Whatever anyone, including the Prime Minister, were to say about "lifetime opportunities", etc., is politics. Parliament cannot be held to that in law.
Politicians lie, exaggerate and obfuscate. None of that puts a legal obligation on parliament. Recognising that is part of growing up.