Literally, it would be: Bumabá ang pag-ibig. However, if you are using it idiomatically, there may be another way to say it depending on your intended meaning.
We don't use accent marks in our spellings, but I placed one in "bumaba" to guide you on its correct pronunciation. Bumabá = to step down; to descend. Bumába = to recede; to reduce/decrease in value or measure.