I'm not sure if you got it by now but The hint for it in game is really sneaky.
Basically you need to do everything on the ride to Munbury trip, protect him at least once, then have sex with him no more than 2 (TOO) times. I would've never gotten it myself without help from here lol. You also need to give him 5 'something' stones (I forgot what they were called) when asked. At least that's what I did.
I actually still haven't got it (cries). I don't know why. I mean, I know I got everything right. I ate him out no more than 2 times, protected him from the 2 emerine golems at turn 11, then just walked around until he was done to give him 5 emerine crystals. After all of that, we'll just go home. The option to "ignore his hand" never appeared the whole trip. What's wrong??? Aozoranokumo said I need to do the discount talk too, and I've already done it. I need help.