Add combined fields to Content type I'm creating a website with a Project content type. In that content type there are common fields and a few group fields. Group fields are fields that need to stay together and can be added multiple times. So in my Group fields there will be a date field and a text field that can be added multiple times.

Do I need to create a new content type or taxanomy type for this or is there a module for Drupal 8 that provides this behaviour.
Try the module field_collection.

Add a field of type field_collection to your content type and allow multiple values. Then go to structure => Field collections and choose your field to add your date and text field.

Update: field_collection is on its way to be deprecated

Use paragraphs module instead.

Notice these meta data issues for paragraphs.