だ [da] is the informal form of です [desu]. It is a (the only?) copula (linking verb, a word that connects a subject to its noun/adjective. Ex: be)
[Is your example a complete sentence or a phrase? But anyway...]
In Japanese, if the subject is clear, it is usually omitted. So in your case, the 'I' is already implied, so 私 [watashi] / 僕 [boku] (you are male, right?) can be dropped.
And if I am not wrong, the same goes for objects as well. It is implied that you are talking to 'your lover', so あなた [anata] / お前 [omae] (you) can be dropped too.
So 'da' 'links' 'I' to 'you'.
よ [yo] is used to make assertions, which means you stress the sentence/fact you are making. It is used by female and (preferably) male.
[Hope I answer your question. Anyone, please correct me if I am wrong.]