There are 3 photos that you have to show Ken to trigger the Ken Samantha Sharing Route if you want to see the whole dialogues from him.
1st Photo: any photo at the Beach
2nd Photo: the third photo in Ken's House ( Samantha shows her ass )
3rd Photo: while you and Samantha having sex
After knowing that you and Samantha having sex with each other, Ken will ask for your help to convince Samantha. Talk to Samantha in her Bedroom and tell her that Ken is a virgin and he's not happy. Talk to Ken again and tell him to just join in the next time you're having sex with Samantha ( Tuesday / Friday )