Thats the problem though we don't know anything about her husband or how that stuff went down. Do we even know if they are actually separated? or if he is just away somewhere I mean Bella still wears her wedding ring doesn't she we know she at least still cares about her husband but is lonely and sexually frustrated hence her fooling around with the MC. If Bella's husband is still around somewhere and alive Jill might not be to happy with Bella cheating on him.
True, we don't know what the circumstances were, but we do know that Bella has "forgiven" him for something and was wanting him to come home, so whatever happened would appear to be his fault. If this is the case, I'd imagine Jill would side with Bella and might not think too badly of her seeking comfort in the arms of another man.
Of course, that "other man" being the MC is where the problems would arise as, like I said, she could go the Megan route of feeling hurt that her best friend and the guy she likes have been getting on but also recognise the positive change in Bella as a result of it and be somewhat accepting of it, or she'll be completely devastated by it and it will ruin her friendship with Bella and end the relationship with the MC. I'm hoping for the former, but that would mean DPC re-hashing a character dynamic from their previous game and I'm not super confident they'll do that.
Also, an interesting thing to note is that Bella isn't wearing her ring after the sauna scene.
Could this be a sign that she's finally moving on?