What should the questioner do regarding his friend who claims to love prayer but abandons it for long periods and does not respond to advice?

Your friend is frivolous and dismissive of prayer, and his claim of loving it is untrue. The warning in the Almighty’s saying applies to him: "There succeeded them later generations who neglected prayers and pursued desires; so they are bound to meet perdition." He is a disbeliever due to his abandonment of prayer, as the Prophet (peace be upon him) said: "The covenant between us and them is prayer; whoever abandons it has disbelieved," and "Between a man and polytheism and disbelief is the abandonment of prayer." The meat he slaughters is not permissible to eat, he cannot marry a Muslim woman, he does not inherit from a Muslim, he cannot enter the Sacred Mosque of Mecca, and if he dies, he is not washed, not shrouded, no funeral prayer is offered for him, and he does not leave an inheritance; his wealth becomes spoils for the Muslims. You must advise him, and if he turns away, there is no harm in parting ways with him.