Tradition

it’s extremely important. pls sis. don’t cheat yourself. allow him to marry you well. you deserve especially if you’ve given birth for him.

can I ask why it is extremely important?

In the eyes of his people you aren't his wife and he can marry another.

If he dies, they will want to take all he left and kick you out. Unless you have court certificate.

However, if you aren't Nigerian, then your own traditions, if you have any, will be followed. However church and or court should be done for certification.

is this Igbo tradition?

yes, it is.