I know we're probably going to get bogged down in semantics again and you and I gave gone over this before, but if Bella's husband were to have cheated on her, and then in a moment of vulnerable weakness she and Jill did something as small as make-out, does that really constitute as cheating for her?
Sure, she may still have technically been married, and even now she still wears her ring and considers herself a married woman, but if that's as far as it went with them, does that small indiscretion after her husband possibly did way more with someone else and their marriage was in dire straits as a result really make her a cheat?
I think something that will clarify a lot of what I say on here will be explaining why I have such an issue with cheating.
I'm not religious, I don't care about the "sanctity" of marriage. I'm not a possessive or overwhelmingly jealous person. I'd have no issue with an open or poly-amorous relationship. I have an issue with the dishonesty that comes with infidelity. I value trust above pretty much anything in a relationship... in most things actually. I need to be able to trust my partner and cheating nearly always involves a level of dishonesty I consider it impossible to recover from. It isn't the cheating itself (though I don't like that at all, I have that same gut reaction of hating the idea someone else is with my partner. I'm not into NTR or whatever...) it's the inherent dishonesty that comes with it most of the time.
If what Bella is doing with the MC technically counts as cheating is separate from whether she's breaching trust in a way that would transfer to me were I in a relationship with her. If James has walked out on her and been gone for a long time without any sort of contact there's no (or severely diminished) expectation of fidelity. I wouldn't hold it against Bella for technically cheating by sleeping with someone else because there wouldn't really be any sensible expectation of fidelity provided she from the point of cheating onwards considers the previous relationship dead. Yes being married is an explicit expectation but I hold little value to being married. It's meaningless to me, it's a legal document that shouldn't impart any trust or security to a relationship. If being married creates trust there wasn't full trust to begin with. Ergo, meaningless.
So even with the marriage I feel at some point you stop being in a relationship and no-contact to the degree James has shown is a sensible point for Bella to consider the relationship over thus there wasn't any dishonesty. I could trust that provided I didn't entirely abandon her for years I'd have her fidelity. However, having slept with Jill creates an automatic breach of trust because she still considers herself married as of Ep1. She still considers herself in a relationship. If she cheated with her and continued to believe she is in a relationship she obviously doesn't consider the relationship over. She doesn't consider him gone for so long to be enough to end the relationship so she's breaching trust. She's actively, consciously, engaging in what she knows to be infidelity and I would have every reason to believe she'd do the same to me.
It's why I'm somewhat (very very dubiously) open to Sage as a partner too. She may well not consider what she's doing with the MC infidelity. It's not unreasonable to consider her relationship with Chad dead considering he wont even kiss her, actively avoids all contact and is cheating on her. She would need a damn compelling reason why she didn't just end things (Bella has the excuse of seemingly total no-contact) but there's a sliver of circumstance I could see myself dating her. I could trust that provided I didn't entirely ignore her, refuse to have sex or even kiss her, I would have her fidelity.
Maya and Josy on the other hand breached trust, lied and it spiralled into further lies. They yo-yo'd back and forth between doubting their relationship, regretting infidelity, being on the edge of breaking up but come Ep4 are playing happy families and living together and not mentioning to one another they both fucked the MC. There's no wiggle room there. They knowingly and consciously cheated on their partner and hid it. It then created a whole mess of lies after the initial one (which is part of why I hate lying. Lies beget lies) and it took the MC to reveal the truth. They never proffered it themselves. They may have had reasons for cheating... but that isn't my issue. It's the lying and a total lack of trust that they wouldn't do the same to me.
So to answer your question. No it probably wouldn't be cheating if James cheated on her and she in a moment of weakness slept with Jill... but it is still a dishonest act because her behaviour after the incident (if it happened) was one of someone who didn't consider the relationship over.
