Can a failed asylum seeker get married in Germany

I am asylum seeker in Germany and my asylum has been rejected twice but I have appealed again. I have a polish woman living in Germany. We are in love. I want to know if it's possible to marry her in Germany despite my negative decision from court in my asylum?  If possible , what document should I bring for the marriage and if I bring my Nigeria passport for the marriage will they deport me with the Nigeria passport?  Thanks

As far as I know, you cannot marry in Germany as long as your asylum application is rejected and you are in an “awaiting deportation” status.
And neither should you bring the unfortunate lady into the questionable situation of being married to an illegal immigrant. She deserves better!
Therefore I strongly suggest you sort your legal matters first, e.g. by cancelling your asylum application (which, for a Nigerian, is anyway almost certain to be rejected), return to your country and apply for a marriage visa at the German embassy there.
This is the best and cleanest way for you!

But I have seen people with negative decision get married in Germany.

Then you can ask them how they did it.