Ran & Shinichi is the most perfect couple depicted in Detective Conan!! They argue, they laugh, they chat on hand phone, they comfort each other, even Shinichi has shrunk to be a 7 years old boy. He will one day return to his normal self because with Technology & Chemistry, you can create a antidote which is permanent to cancel the APTX 4869!! Even if Shinichi has to wait for 10 years...to allow Haibara to create the antidote. It's just similar to the Empty House in Youtube:

http://www.youtube.com/watch?v=YIJBzRmLk6g&feature=related

http://www.youtube.com/watch?v=rQF5OaMIMd8

http://www.youtube.com/watch?v=z6heLyub-i4&feature=related

http://www.youtube.com/watch?v=d_RxLjwghFQ&feature=related

He used Edogawa Conan to protect Ran, Kogoro Mouri, Professor Agasa, his father and mother from Black Organization's wrath!! So, he uses 2 identity, when he drank Chinese wine and use Haibara temporary:
Episode 48 to 49, Episode 190 to 193, Crossroad in the Ancient Capital and etc...