Alison is supposed to be a bit plain and awkward and Ian doesn't seem to be a big boob guy.
Almost every scene Ian can emphasize how obsessed he is with Alison's boobs, and her boobjobs always get him going. It's Alison that can be slightly annoyed by his obsession, thinking it's the only thing he likes about her. So, yeah, missed the mark on this one.
Also, I wouldn't count one comment teasing Alison about her clothes (saying that Cherry's style is more appealing) as Ian's general preference of Cherry to her. Obviously, he has to ignore Alison's advances to go for Cherry since these relationships conflict with each other, but the player can ignore Cherry and go for Alison, and his reaction to her sexy yellow dress is by far the most complimentary out of all girls. He even gets a bit insecure thinking she'll get everyone's heads turning. So, I'd say at times her raw sex appeal can rival Ivy's when it comes to Ian's reactions.
Holly is plain and he is mostly interested in her intellectually and romantically.
Another thing that depends on external factors. Initially it is true of course, but Holly can demonstrate just how sexual she can be. If holly_change is of high value, then Ian is surprised by Holly's bold moves and dirty talk, turning him on quite a bit and making him eager for more. He's not only interested in her romantically and intellectually, but he also can't get over the fact just how eager she is to please him and listen to his instructions. So, you could say she awakens a dominant in him with her deliciously submissive attitude. Also, he can break up with Alison for her (instead of the other way around), so I'd say that evens them out a bit.
The "cheating" scenes are already there though, in an open relationship with Lena, Ian can still fuck around with Alison.
No, he can't. He can only fuck around with Alison if their relationship is casual (just dating, not being a couple). So he doesn't cheat on Lena with Alison because they're just fuck buddies.
