What does lemented mean?

"Lemented" is not a word in the English language. It's likely a misspelling of "lamented."

Lamentable means something that is regrettable, unfortunate, or deserving of sorrow.

Lament is a verb that means to express sorrow or regret.

So, if someone says "I lamented the loss of my friend," they are expressing their sadness about the loss.