Hello @ Donmorris,
Thanks for reaching out to the Wefugees community.
Marriage and asylum are two separated issues.
If your asylum was rejected, but you still fear that you will be politically persecuted in your country of origin, you can make a second asylum application in Dortmund, which has to be well justified, e.g. you have to show how the situation has deteriorated. Otherwise it will be rejected as manifestly ill-founded at once. So I recommend you to seek the help of a lawyer.
As far as your marriage is concerned, I've inserted a link to the marriage regulations in the Netherlands. It will hopefully give you the information you need to get a picture about what to prepare: https://www.iamexpat.nl/expat-info/family-kids/marriage-netherlands.
Regardless which country you marry in, you'll have to apply for a visa for subsequent immigration of a spouse in the German embassy of your home country, except if you have a legal here.
I hope my answers were useful for you and I'll be very pleased if you contact me again with further questions. I'm a member of the MBEON-staff and I‘ll be glad to guide over a longer period of time. Mbeon is an online consultancy for migrants via the mbeon-app, which you can install on your smartphone for free. Download it via App Store or Google Play Store. You'll find me In the mbeon-app under my name „München, Frau Müller“ and get confidential one-to-one advice in a safe virtual room where nobody can wiretap messages. Further information: www.mbeon.de.