Gitlab ist overlaying all subdomains and even my entire nginx.config – Debian

I am pretty new in those server / cloud dev things.
So I rented a vServer and started playing around. First with nginx. I made my own config and all went well, getting the right html files on the right sub-/domains:

    server {
            listen 80;
            server_name beispiel.de;

            location / {
                    root /var/www/beispiel;
                    index index.html;
            }
    }
    server{
            listen 80;
            server_name gitlab.beispiel.de;

            location / {
                    root /var/www/beispiel/gitlab;
                    index index.html;
            }
    }

Then I wanted to run my own git repo via gitlab, and I installed it like shown this tutorial:
https://www.howtoforge.com/tutorial/how-to-install-gitlab-on-debian-8/#install-the-prerequisites

Gitlab is running smooth. But my problem is now, that it overlays all subdomains as well as the domain itself. My config I wrote earlier seems skipped by some kind of second nginx, installed with gitlab.

I tried to stop it by service nginx stop but as I tried to service nginx start again this was the response:

Job for nginx.service failed. See 'systemctl status nginx.service' and 'journalctl -xn' for details.

So I htop-ed and saw that nginx processes where still runnung. I killed them, but they always autostarted again.

systemctl status nginx.service
● nginx.service - A high performance web server and a reverse proxy server
Loaded: loaded (/lib/systemd/system/nginx.service; enabled)
Active: failed (Result: exit-code) since Tue 2019-12-17 14:58:43 CET; 3min 48s ago
Process: 13257 ExecStop=/sbin/start-stop-daemon --quiet --stop --retry QUIT/5 --pidfile 
/run/nginx.pid (code=exited, status=0/SUCCESS)
Process: 1539 ExecStart=/usr/sbin/nginx -g daemon on; master_process on; (code=exited, 
status=1/FAILURE)
Process: 1537 ExecStartPre=/usr/sbin/nginx -t -q -g daemon on; master_process on; (code=exited, 
status=0/SUCCESS)
Main PID: 13321 (code=exited, status=0/SUCCESS)

Dec 17 14:58:40 v2201912109976104637.goodsrv.de nginx[1539]: nginx: [emerg] bind() to 0.0.0.0:80 
failed (98: Address already...use)
Dec 17 14:58:41 v2201912109976104637.goodsrv.de nginx[1539]: nginx: [emerg] bind() to 0.0.0.0:80 
failed (98: Address already...use)
Dec 17 14:58:41 v2201912109976104637.goodsrv.de nginx[1539]: nginx: [emerg] bind() to 0.0.0.0:80 
failed (98: Address already...use)
Dec 17 14:58:42 v2201912109976104637.goodsrv.de nginx[1539]: nginx: [emerg] bind() to 0.0.0.0:80 
failed (98: Address already...use)
Dec 17 14:58:42 v2201912109976104637.goodsrv.de nginx[1539]: nginx: [emerg] bind() to 0.0.0.0:80 
failed (98: Address already...use)
Dec 17 14:58:43 v2201912109976104637.goodsrv.de nginx[1539]: nginx: [emerg] still could not bind()
Dec 17 14:58:43 v2201912109976104637.goodsrv.de systemd[1]: nginx.service: control process exited, 
code=exited status=1
Dec 17 14:58:43 v2201912109976104637.goodsrv.de systemd[1]: Failed to start A high performance web 
server and a reverse pro...rver.
Dec 17 14:58:43 v2201912109976104637.goodsrv.de systemd[1]: Unit nginx.service entered failed state.
Hint: Some lines were ellipsized, use -l to show in full.

I don’t know what to do.
Can anyone help?

Kindly,
a noob 🙂