The words "Thank you" are a mere conversational expression of gratitude. They fall flat over time. They fail to convey the appreciation I have of you.
When we first started falling in love, just after we first spoke the words to one another, I told you in a poem that when I say "Thank you", I really mean "I love you." I still do that.
I will spend the rest of my days in a valiant struggle to bridge the gap between the words "Thank you, my love" and the gratitude I feel.