Ok so u need to find the right beat to the song in a way that's either good or happy. If its a happy song u may want it to be like a not fast beat but a moderate tone or rythem. If its a sad song, the song is normally going to be normally slower and the tone to it may be kinda low or depressed because its sad. With love songs it can be both but depending on how ur writing about her u may want to look at the beats of the song or the rythem. U could look up different types of love songs on YouTube and see if u could find a great beat u want to write your song to.