She never sleeps.(correct, simple present)
She never sleep.(wrong, she never follows v1)
She never slept.(correct, simple past)
I never live. (correct, simple present)
I never lived.(correct, simple past)
He never loves.(correct, simple present)
He never love. (wrong, he never follows v1)
He never loved me.(correct, simple past)
Never happen/happened.(both are correct)
He/she/it/any name are followed by verb form5(v5).
I/we/you/they are followed by verb form1(v1).
sleep(v1) slept(v2) slept(v3) sleeping(v4) sleeps(v5)