This particular approach wouldn't work well with what I have in mind: Tara is genuinely the heroine of the story, and she is undergoing positive character growth. Your suggestion is akin to a usual fantasy hero who eg overcame his cowardice in the first part of the story to suddenly become craven again. Possible, but I personally rarely like any "backsliding" like this. And yes, in te context of this story, being monogamous is a moral failure (but cheating is also bad). [Tara might still re-marry at some point, just without any assumption of exclusivity.]Now there is one possibility, but feel free to discount if it doesn't work with what you've got planned, is have her "start again" with another man. Perhaps there's a plot path where she meets someone who makes her doubt her current path of debauchery or something, players could choose to put her in a relationship and then cheat on him as her corruption is too strong.
But! Most of my objections only pertain to Tara being the wife in the scenario you mentioned. And you gave me an idea for one of the liberation story arcs in Chapter 2 that I like more and more. Tara might meet a woman in a bad/emotionally abusive marriage, and help her break free. And I already quite a few details about how that is going to work out. Only downside is it would take again quite a few scenes to tell that story.