Not that she totally couldn't violate that but you have to have some trust right?
Has she done anything to earn that trust? You don't know for a fact that she's not still seeing Señor New Guy--she just told you she isn't. I don't remember...did she lie about it before? You may have just invited that problem, and all of the pain associated with it, into your home where you'll have to look at it every day.
She made no commitment to you or to the marriage. All she wants is a place to live while she "works on herself" to become a "happy person." I'm not sure that D3 is your top motivator here, because if your W divorces you, the households will be split anyway. I think you accepted her proposal on the off chance that perhaps, maybe, in the future, after she's had some time (with you paying the living expenses), after she gets happy, she'll want to work on your marriage.
I think this puts you in a very weak position in the present and in the future. In the present, you're playing "daddy" to your W with no accountability. If, by chance, she does decide that the marriage is what she wants, you've fed her sense of entitlement.
Maybe you're strong enough to establish and enforce boundaries in that kind of situation, but I know I'm not.
