How Many Sects Can You Actually Join?
You are only allowed to join 1 sect at a time and you can try to leave and join another sect but with penalty depends on what sect you joined in.
Once you’ve learned everything you need, you may choose to leave the sect for good. Once you’re out, you’re out permanently.
The old man sect is different, you cannot leave unless you meet certain condition.
Completing the sect quest to a certain point allows you to retain your relationship with the NPC of the sect.