Unfortunately, some priests give bad advice. Popes too apparently.
No one has ever been allowed to receive Holy Communion except Catholics in the state of grace.
It is objectively speaking a sacrilege to receive improperly, though in your case it sounds like the priest is guilty of it, not you, since you sought advice in good faith.
At any rate, you cannot continue to receive Communion anymore unless you go through RCIA and receive the sacrament of Confession.
Make a “spiritual communion” from the pew instead.
Prior to Vatican II? Yes.
You need to read the 1983 Code of Canon Law. Non-Catholics ARE allowed to receive communion in certain circumstances.