Adam has been Heavily augmented. More so than MOST of the other people you encounter in the game. This is meant to seperate him from the rest of humanity. So to enhance that seperation you won't see him interact in a meaningfully emotional way that isn't anger with another person, save for the person established in the beginning of the story as his romance (whether they're "established" or not). Also given the fact that for most of the game he believes (though I figured it out really early on, but I think your meant to) that the woman he loves was murdered and her body burned beyond all recognition. He should feel well detatched from humanity at that point. Most people would not survive that trauma emotionally, or mentally. In all likelihood, whoever you had been before all of that happened, would be dead. And actually, in Adam's case, this is still more or less true.
His entire standpoint on life, augmentation, morality... it's all mutable based on your choices after he's augmented. Opening mission Adam kills the intruders, and you're not offered a less-than-lethal alternative to gunfights, except attempting to avoid them entirely. After being augmented you receive a plethora or non-lethal options, along with quite a number of new lethal options as well.
But long-story-short, I don't think it would have helped the story, and in fact probably would have hindered it, for Adam to take a real interest in any other females. It would bring about questions as to what's driving him forward other than finding and bringing to justice Megan's killers, and it's painfully obvious throughout the game that that does seem to be his sole motivation (until he switches to finding her as his motivation).
But let me ask you, if you got FUBAR'd like Adam did... 90% of your body replaced with mechanical versions of former pieces, the woman you love was dead, and not only dead but her body incinerated beyond visual identification, and not only that but you felt as if you failed to protect her...
Would you want to go get laid?
Pretty much longer version of what I said and I agree.