It's been a bit since I've played so it's not fresh but I think Allie started to be more career focused at some point in the marriage and especially after the divorce. She attracts attention but doesn't act on it since her focus is career and Lily.
Yeah, its pointed out in the game nonstop (esp by jasmine but by natalya too) how EASILY allison could score any kind of guy she wanted (just not this one specific asshole ...).
The devs made a point in showing that allison installed "tinder" on her phone but never did set up a account.
Camille tries to play wingwoman for allison when they go out but instead allison is home early and sends the mc (unintended) pictures instead of meeting other men.
It couldnt been more obvious that there is only one guy allison wants, shes not over him at the beginning of the game and thats why shes still this angry.
Despite the cheating, her divorcing jake and everything shes still hoping that jake is somehow able to make her forgive him and get her husband back. And saving lily's life is probably one of if not the only thing which will be significant enough to overlook the cheating and work on a better relationship than it has been in the past.
A lot of people are annoyed by her behavior but i would consider her a worse LI if she would be less confrontional and emotional about the whole thing. It shows that she still cares, shes still hurt which wouldnt really be the case if she would have been able to move on (which would have other readers made to like her more).
Her being all "Yeah well, we both fucked up, lets just not talk about it anymore, who cares" in the beginning would have made her such a weak, meek and pathetic LI.