NGINX SSL: error:0200100D:system library:fopen:Permission denied
There is only one suggestion, you don't have enough rights for access file /etc/nginx/ssl/mysite_com/mysite_com.crt. When you start nginx -t under your account, nginx started with your permissions and couldn't get access to this files. There is two ways how to fix this issue without changing anything. First one - run nginx -t under root account or trough sudo to test configuration, second one - run nginx -t under http account to see how nginx start in real environment. But if you would like to make changes, you could add your user to group http and try to run nginx -t.