I'm sorry for writing to you, but I just have to tell you how lovely you are, and that I like you so much. I can't stop thinking about you. Thank you for being you. You are amazing.
Remarks about the translation
if it is better to use other words in the translation, just do that, as long as it means the same.
Oprosti što ti pišem,ali ti jednostavno moram rijeći koliko si draga osoba i da mi se jako sviđaš.Ne mogu prestati da mislim na tebe.Hvala ti što postojiš.Ti si nešto posebno.