Not to wade in too deep, because I haven't read through every page in the last few months to see if it's already been brought up, but I tend to doubt the reason for Bella's marriage being broken up was due to Jill in any way. For one, the way Bella talks about her marriage ending it strikes me as an event that happened further in the past than a year or two ago. She also seems comfortable with Jill more than anyone else, which I would find hard to believe if Jill broke up her marriage. This doubly applies to Jill, who isn't perfect but does seem to be the most "good" character out of any of the main LIs.
I'm not saying this doesn't mean that they did something (I think it could go either way), just that I don't think it was while Bella was still in her relationship with James.
I'm not saying this doesn't mean that they did something (I think it could go either way), just that I don't think it was while Bella was still in her relationship with James.