Denmark Maastricht Treaty: after a referendum rejected it, opt outs were negotiated and the Treaty was approved by referendum with the opt outs
There was no referendum in Italy on the Nice Treaty, or if there was evidence appears to have disappeared from the net. Maybe it’s a beneficiary of the right to be forgotten law.
France and Netherlands: Constitution was dropped. Replaced by less ambitious Lisbon Treaty.
Italy: same comment for Lisbon Treaty as for Nice Treaty
Greece: Euro bailout referendum The rejection of the bailout package was a referendum held in Greece only for an agreement affecting all member states of the Eurozone. They did not wish to change the terms of the bailout and how would it be democratic for a vote in one state to override the wishes of the elected governments in other states. The elected Greek government was free to choose to leave the Euro if it was not willing to accept the terms for a bailout, The elected government and the national assembly chose to stay in the Eurozone and continue bail out negotiations on terms acceptable to the other states.
All states choose freely to remain in the EU apart from the UK, which has not provided a brilliant example so far of the advantages of withdrawal. When the UK voted to leave, the EU respected the result and entered into negotiations while the UK Parliament failed to agree on a withdrawal plan. States which stay in the Union are to some degree constrained by other stages of the union, as applies to the member states of the USA or the states which make up federal Germany.