I often see "loose" in sentences like "loosing my mind" "I don't want to loose you" "The sun looses its fire" and so on... As you see, it must be "lose"? And "losing my mind" "I don't want to lose you".

Lingvo says it must be "lose", dictionary.com (EN-EN dic) tells me the same. But anyway...
What's the matter with these two words? Who is right and who is wrong?