Is taking Melatonin bad?

Here's the backstory and don't judge. No one is safe from addiction.

Three weeks ago, I had the flu and my boyfriend bought me some Gravol. It knocked me right out and I have had problems sleeping for a few months. I loved the way it could make me sleep so easily. I started taking Gravol simply because I was bored and didn't have anything better to do was sleep. Then I started wanting more and more, and I started getting scared because I've never felt that way taking pills. I talked to him and my mother and I told them I thought I was addicted to it. They both agreed and I've gone cold turkey on it since.

I talked to my aunt about the addiction and she lent me some Melatonin to try. She said it's not really like taking Gravol because it's a vitamin. Now, my boyfriend is worried, he said it's still taking pills and it will mess with my natural sleeping habits and it will replace them with unnatural sleeping habits, if I take pills to sleep.

Is Melatonin okay, or is my boyfriend right?