See my tagline?
I truly believe it. I do think we are accountable for our own happiness, and that we can nearly always find ways to improve or add to our happiness.
Of course I’m not so naïve as to think it’s just a question of deciding to be happy, but it is a decision to evaluate where you are and then take actions to get to a better place. Maybe not "happiness" as in how we might feel at some ride in a theme-park, but rather "happiness" as being one step closer to being content with where we are.
Your partner is offering you something. Your options are basically to accept her offer or refuse it. I have a feeling that for her it’s easier: She has decided to not end her affair, and is now waiting for you to accept that. Hoping that some belief that maybe some day in the future she will chose you – and you will still be there waiting for that day.
I can share that there are numerous examples in history of a spouse "accepting" their partner has a lover. There is a certain "agreement" not to question the spouse when they go "fishing" late into a Saturday evening (even if they never take their gear with them), and an expectation to be discreet, shower and use protection. You can find online old recordings of a French presidents funeral where his wife walks behind the casket along with their kids, and a few feet behind them the mistress with their daughter. It’s some version of what I think your partner is offering you now.
You mention that your lives are impossibly entwined.
Maybe a good first-step for you is to untwine. Maybe to evaluate the business, the debts, the assets, the business… Maybe clarify the picture so that your personal relationship is no longer controlled by the business part of it.
Maybe a good first step is to talk to an attorney, seeing as she’s your partner (thereby assuming not married). In whose name is the business? Who is on the hook? Who is the income generator, and who is the management part.
Maybe evaluate what it would be if you both arrived at work at 8:00 and left the office after work to go separate ways. Maybe create a clear distinction between work and home.
Basically separate the business and the personal. Make it clear what debts are business, and what debt is personal. Seeing as not married then who is on the hook for each.
Who knows – MAYBE you can just walk out leaving her with it all – and restart somewhere else. Or maybe you can just fire her, and assume all the debt into a business that you can own, manage and run by yourself. Maybe.
Doubtful… chances are there is some entwinement but at least gather info to simplify that.
I fear you might use the "impossibly entwined" issue as a reason to remain in this personal relationship despite her ongoing affair. It’s a business-oriented version of "have to stay for the kids" and/or "can’t afford to divorce".
There is no shame in reconciling.
IF your partner decides she wants YOU, and if you two work out what works for you then there is no shame in doing that. But while she is in any form of contact, or is pushing for permission to be with OM… then you don’t have the option of reconciling – unless you are willing to change your requirements.
Maybe you just tell her "no thanks. I'll sit out this dance."