Simply replace the unfilled areas such as "" and "[date]" with your information.
I cannot begin to express my gratitude to you. [Help Provided] was one of the most thoughtful things anyone has ever done for me. Your help, allowed me to [accomplishment]. This would not have been possible without you.
It means so much to me that you would be there in [my/ my family's] moment of need. It gives me great hope to know that people can be so giving and thoughtful. You are an example to the rest of us. If there is ever anything I can do to return the favor, please do not hesitate to ask. If you ever need me, I will be there.
Thank you again.