I'm assuming that this line means that Love can happen quickly and you never know how long it will last and if it ends, forgetting it takes time because you were just in love and now it's over so you have to take time to processs that it's over and forget what you've been through. Sorry if it doesn't help.
Answer:
The last one
Explanation:
the last one, or, rather, D.
Zealous means with zeal. It means with enthusiasm
