Assalamao Alaikum Wa Rahmatullah
Alhamdolilahi Rabbil ‘Alameen Wa al-Salato wa al-Salamu ‘Ala Sayyidina Muhammadin Wa ‘Ala Aalihi Ajma’een.
It is an Islamic principle that a Muslim should be regarded a Muslim and a non-Muslim as a Non-Muslim.
To regard a Muslim as a Non-Muslim and vice versa is a grave sin and will lead to Infidelity (Kufr).
One should to tauba and stick to the principles of the Deen.
Allah Knows the best!