I figured it out. You have to deny going to the garden when Ashton freaks out from the interruption on the TV(?) and then it'll appear.
Viewing post in Picture Perfect Boyfriend (updated) comments
It SHOULD be that John appears after the first two photos are gotten AND you've gone on at least two dates, kind of an incentive to pick other dialogue options since you get stuck with Ash again. At least that's how it SHOULD work, some things may have gotten switched around as I sometimes forget my own programming.