I love this and I like your thoughts about what would make them trust each other. In my head, them coming to trust each other did not happen in one great moment but in a shit tone of smaller ones. In some stories I see them revealing their back stories or confessing their secrets in one night of intimacy and that brings about trust. I think that wouldn't work for them because they both know how easily that can be A. faked and B. broken. To me, trust for them comes over months, even years, of just having each other's backs. It would come in the little moments of honesty. Only after working together for quite some time would they begin to trust each other professionally and then even longer for personal trust. They are the type of people that need to see that trust in action.