Adding to BloodyMares’ first point: Alison, like the rest of the female cast except Louise, don’t care about Jeremy at all, while she’s got strong feelings for Ian. So if she’s choosing one guy to be exclusive with, she’ll choose Ian without hesitation. But if she’s choosing one guy to hook up with non-exclusively, she’ll choose Jeremy because she won’t end up having her feelings hurt in the process. And if Ian makes out with Emma and then takes her home, it proves to Alison that it’s the latter choice she’s making. So she’s choosing the gigantic dildo with a human body attached to it. Ian being more than a human-shaped dildo is an advantage in some situations, and a disadvantage in others.
Emma is different, because she’s seemingly not interested in a relationship, and the way Ian takes initiative proves to her that his priorities are the same. And in the long run I bet Ian will get the chance to sleep around more than Jeremy anyway. If you choose to keep the relationships with Lena and Cindy non-romantic, Ian can already be involved with those two plus Minerva and Emma, maybe even Cherry, without any of them likely caring about the others. Ivy, Louise and Jess will probably also be similar alternatives in the future.
Several of those wouldn’t be interested in Jeremy no matter what. And the only woman who’s interested in him romantically, is the one who completely, fundamentally misinterprets his character. I’d say Ian’s options overall are far better than Jeremy’s.