There comes a time in most relationships (sentimental or not) when the parts involved simply do not trust each other anymore.
No matter what they say, no matter how hard they try, no matter how much time and resources you spend making their case.
Actually, continuing to state the case in these situations is futile. Chances are the main arguments, values, plans are at least part of the reason why the distrust started developing. So, if that’s all each part has to contribute, the relationship is over.
The only thing to do in these cases is take a step back.
Open your mind, listen, apologize if needed (it usually is). Be critical of your original stance and see if there’s still space for a part of it.
Relationships, as most things, evolve. When you do not evolve with them, you are out.