Help, How can I deal with jealousy?

Ok, so this girl that I'm in love with is in my cl. Everything about her is perfect. My friend that used to be my best friend but he's barely my friend now is sits next to the girl that I'm in love with and he flirts with her and does stuff like that. Their is also another thing that I'm jealous of about him that I will leave unknown. Help. How can I get the girl that I really like. I feel like doing oxy again and other drugs since I'm kinda depressed now. Help!!!