James is fucking dead so stop mentioning him.
It's fair to presume that he's still alive given what Bella says/thinks about him. She wants him to come home, says that she forgives him for something he's done, wonders if he'd forgive her for what she's doing with the MC, etc. If he were dead, this would be some seriously psycho denial that Bella is going through and as much as people joke about this kind of thing, I really don't see DPC having Bella be like this.
James's return is perhaps one of the most obvious impediments to the MC's relationship with Bella, and just because it seems so obvious doesn't mean it's not possible. I get that as a Bella fan you wouldn't want that, but it is very likely.
Now there's speculation that the marriage may have ended because of Bella having a one night stand with Jill, but I'll ask you all honestly, if your wife (future or current) was making out with another woman, would you leave her or explore the possibilities?
Just because we're all horny idiots who like a bit of girl/girl action doesn't mean everybody is. It's not necessarily as simplistic as "my wife likes girls, let's explore this and try to save our marriage".
Perhaps James cheated on Bella because he felt that she wasn't as interested in him and their marriage anymore (which could explain the "how long has it been" comment from Bella), and then when the affair came to light, Bella convinced him that that wasn't true and that she did still love him. So they stayed together and tried to work through their issues but it wasn't going well, and then if there was indeed a drunken moment of intimacy between her and Jill that James walked in on, it would only serve to compound his belief that she was no longer invested in their marriage, hence why he wouldn't exactly be wanting to strip off his clothes and join them.
And if he did leave her (for whatever reason), apart from being a little harsh, Bella enjoys a fairly healthy lifestyle (wine with friends, yoga, reading) plus she's a teacher as well as the librarian. Would a person with this kind of healthy lifestyle be all nutty about a husband that left 3 years ago?
When a marriage breaks up, denial, hurt and anger are common initial reactions, followed by acceptance and then moving on (moving on doesn't necessarily mean going off looking for a new partner, but it means letting go of the old one).
But death, death is different. You don't hate the person for dying (although some people think this at some point in their grief, but they don't harbour it for long), and although the vow is "'till death do us part", a lot of people do feel like they are cheating on a deceased spouse and take a long time to move on.
I still can't see that Bella would be pining after her husband if he left her 3 years ago. By my reckoning, he's dead.
Sometimes a break-up, especially a marriage break-up, can be like the experience of grief and it can take years for a person to get over that loss, if they ever do get over it. Not everybody is so willing to move on from a long-term relationship so easily or quickly, and some will even hope for a reconciliation with their ex even if that ex has moved on.
We also don't know exactly how long has James been gone. People keep coming back to it being 3 years, but what she said was:
"How long has it been since a man did this to me?
"Three years?"
"No, that can't be right..."
"I haven't gotten an urge to touch myself...that's all..."
"Until tonight..."
This doesn't necessarily mean that James has been gone for 3 years, just that, for whatever reason, she hasn't felt this much desire for a man for 3 years. Something could have happened to her years ago which caused her to lose the desire for sex (no, not a miscarriage), and this cold fish attitude could be what drove James into the arms of another woman. So maybe he's not been around for 2 years, 1 year, or even just 4 or 5 months. In any case, Bella not being able to accept or let go of him is entirely possible regardless of how long it's been.
I also want to know why Nick says Vinny dropped out last year but he doesn't say that it was to deal drugs.
First of all, we don't know what really happened with Vinny even if it seems likely that he got caught dealing drugs and was expelled, but if this were to be the reason then it's probably covered by the DIKs secret code so Nick can't tell the MC the real reason that Vinny's gone.