It turns out Sam Alito hates the Constitution as much as you thought he did.
Summary
Justice Samuel Alito, a self-described Originalist, has been criticized for allegedly disregarding the Constitution’s text when it conflicts with his personal views.
Recently, it emerged that Alito accepted a knighthood from a European order, despite the Constitution’s ban on foreign titles for U.S. officials.
This title, from the House of Bourbon–Two Sicilies, raises questions about Alito’s commitment to American democratic ideals, which the Framers aimed to protect from foreign influence.
Critics argue that Alito’s actions reflect hypocrisy in his supposed adherence to Originalism and constitutional principles.
Those were honorary knighthoods that generally mean nothing. OPs article claims that Alito pledged "an oath to the Sacred Military Constantinian Order of Saint George." That is an entirely different thing if true. As the saying goes, a man cannot serve two masters. If he has pledged an oath to this order and the Constitution of the United States of America, which takes precedence in his mind?
I would find it uncompelling if this wasn't one of 9 people we trust to actually enforce the Constitution, and it was just their religion. No he knew this was unconstitutional and sought it out anyways.