*shrug* Afraid this game has at least a few of these "why?" kind of pre-reqs - i.e. for some reason, if you've ever earned a single heart / expressed potential emotional attachment to Ian as Lena, (including just cuddling after sex - kill me, I'm a post-coital cuddler!

) you can never kiss Holly at all, (even if Ian's never expressed the slightest interest in Holly). You can select the option, but you always get yoinked back and it says you don't really want to do that. You can do anything you want with pretty much any male in the game and no issue, but kissing a woman? Madness!!
Correction - apparently if you've done anything whatsoever with Ian, you're locked out of Holly. <-- Is sad.