I'm desagree with the answers.... Usually "tonta" means "stupid". But, often, we use in a kindly sense.....perhaps with love. When you are with someone you love...and you make something special, susprise..etc.. Perhaps the other person say you "tonta". It is meaning that the other person like very much the think you do...Like: "it was no necessary, but i like very much you did it for me....and thanks a lot for that"

As for your first question, yes, it means "stupid". As for your second question, I would say "no". Whoever calls you stupid is not thinking in your best interest. Why would you allow that person to make you feel bad. On the other hand, I would recommend spending time with people who appreciates friendship.

No, it also means "silly." Depende de como se diga...