That's a tough one! It can be difficult to find the right words to express how much you care about your best friend. Here are some suggestions for what you could write on the Christmas card:
• Thank you for being a great friend and always being there for me when I needed you most.
• I'm so grateful to have you in my life and look forward to many more years of laughter and joy together.
• You make my days brighter with your infectious smile and positive attitude.
• I'm so lucky to have someone like you who always knows just what to say when I need a pick-me-up.