So, imma just repost my own comments since I can't bother to write it again but basically I think James is long gone.
The theory I find more believable is that they lost a child, James chose the cowards' way and offed himself, Bella was left all alone, met Jill in some kind of therapy session because they both lost someone (Jill lost her sister) but nevertheless Bella never fully recovered.
This could explain why Jill is so important to Bella, why Bella both asks for forgiveness and says she forgives James, and why she has so much difficulty in letting other people into her life.
Also, in EP9 although not much, we do have some additional context, nowhere during her talks with Bella Jill seems to think of James as a problem.
If you don't pursue Jill, she doesn't seem to have a problem with their relationship, she finds it a bit weird but what she's angry about is the dishonesty from both Bella and MC towards her, if Bella really was cheating, there's no way holier-than-thou Jill would be okay with it, it'd really go against what we've seen from her character so far, just look at the way she reacts if you tell her that her friends are cheating on each other.
So, regardless of what happened between Bella and James, I really don't think MC will ever have to face him.