Forsake is a literary word which can mean 'leave',but it means to leave someone forever ,especially when they need you.But 'leave ' to go away from someone or someone for a short time or preeminently.

1) benefit or interest (esp in the phrase for (someone's or one's own) sake) 2. the purpose of obtaining or achieving (esp in the phrase for the sake of (something)) LEAVE To abandon Eg: leave home; left her husband.