LOS ANGELES: The 35-year-old actor is smitten with his 30-year-old girlfriend Mila Kunis - who he has known for 16 years - and plans to tie the knot with her as soon as his divorce from Demi Moore comes through.  A source told Us Weekly magazine: ''They plan to get engaged soon. Being with Mila brought Ashton back to who he really is.  ''He's not playing the field, he's focused on enjoying Mila and the happiness she brings. She doesn't get jealous like Demi used to. He calls her because he wants to and when they're apart they talk constantly.''–SP