even if I have to use my entire credit card, which I did

  • Whenever he releases a product, I always buy it no matter what. (even if I have to use my entire credit card[color=red], which I did)

Should there be a comma there? Because it’s kind of like “even if I have to use my entire credit card, which I did use my entire credit card.”

Yes, but the parenthetical remark should be incorporated with the rest of the statement.

You could do it like this:

  • Whenever he releases a product, I always buy it, no matter what - even if I have to use my entire credit card, which I did.