Dear ....,
I am writing to you this letter in a humble attempt to express my gratitude towards the unconditional support that you have given during [my project, my sickness, etc]. I am truly thankful and appreciate your efforts. I could have never made it without you. It is always good know that l am surrounded by [loyal] and companionate people like yourself. You are a good friend and I take pride in our relationship. I don t know if I will ever be able to return back the favor, but in case I couldn't , please know how much I value and appreciate your help. Thank you very much. Sincerely,