I don't see any warnings on the site about a hack. Even so, it never hurts anyone to be sure their passwords are both strong and unique.

Try asking FetLife if they can recover your profile from a backup. I'm guessing they won't though, unless the hack was their fault.

It's possible that someone simply figured out your password, especially if it was shorter than twelve characters, or just a word, or a word with a number, like most people tend to use.

Someone I know got hacked and his was military grade password

That doesn't sound good. I hope FetLife figures out and corrects the weakness, if it's on their end. Otherwise they could end up with a whole lot of upset users.