Please-
I married in Nigeria. And want not to be married. I spoke with my Priest and he said the Catholic Church does not see it as valid. But he wasn't sure if it is legal in our country.
Is it legal?

If it was legally performed in Nigeria, it will be legal anywhere else.

I am surprised why does the catholic church not see it as valid ? They view any marriage as valid, that is why you have to get an annulment to get remarried,
They may not view it as a christian wedding if not done in a church.

As for as a legal wedding, if you meet all of the legal requirements to be married in that nation you are married