I've now planned 4 main paths for the MC and Jane and one of the paths really requires them not being married. It would definitely mean a reason to keep them together, but it also gives a lot more power to Jane which I don't want.
If you were married, I think there is a lot Jane could do to get the MC arrested/fired depending what he did and stop a divorce.
For example, if she hated you and you went off with Penelope, if she called the Police and lied and said the MC had been sexually involved with Penelope from when she was very young and she'd been groomed and the MC had threatened to kill her if she told, it would destroy the MC's reputation and likely cost him his job even if not proven or he was acquitted. Same with his drug money, dating Mercedes when there is to a very small degree a teacher/student dynamic etc.
I didn't want to open up all of these as they'd be in court for the divorce where some of these things like money would certainly be brought up, whereas she'd have to directly go and involve previously uninvolved authorities with the end of an engagement which means I can see it being more realistic leaving a 'Wife Blackmailing MC' path out, especially as it is a path I don't really have an interest in making.
It is quite important for one of the wife's paths for them to be unmarried too