Unlimited values for 2 combined fields
You can wrap the fields in a Paragraph with the paragraphs module. I.e. create a new paragraph type, repeatable_date, with two fields: date and comment. Then add a new paragraphs reference field to your article and set cardinality to unlimited. This will allow you to add unlimited repeatable date items, each with date and comment.
Or you can create a new custom field type that has a date field and a comment field. This is more difficult to do, but may be preferable if the paragraphs route doesn't suit you. See How to create a new field type for details.