Did you check the CG gallery if you've completed them all?Bad ends don't get CGs, though some friendship endings do.
I have the gallery full
Then you've already gotten all the relevant endings. There are some endings there where they don't end up married, right?If you really want a 'bad end' without CG (it's a bleaker ending than the others), when there's a choice to trust him or not, pick -don't trust him-.
Thank you