A popular online dictionary defines religion, usefully, thus:
Religion: A set of beliefs concerning the cause, nature, and purpose of the universe, especially when considered as the creation of a superhuman agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs.
So then. Is atheism a religion?
Atheism is a singular lack of belief in god/s.
It says nothing in and of itself about the cause, nature or purpose of the universe. Does not posit superhuman agency and has no devotional or ritual observances. In and of itself it says nothing about a moral code or the conduct of human affairs.
Is ‘being in a relationship with Jesus’ a religion?
As such you believe god is the cause of the universe and that by nature it is a creation with the purpose of testing mankind for his worthiness of access to a supernatural afterlife. You consider it the creation of a superhuman agency and you most likely pray and observe religious holidays in the manner determined by your faith. You believe, laughably, that the Bible contains a moral code for the conduct of human affairs.
That IS a religion. Christianity.
Other things that aren’t religions:
Science: A process of evidence gathering and testing to approach a usefully objective understanding of the universe.
Secularism: The singular belief that church and state should be separate.