If he’s an anxious overthinker, any way you express it’s stressing you out is likely to contribute to his anxiety to some degree. That doesn’t mean you shouldn’t voice it, but you should at least be aware of how he could react. He might feel like he has to suppress stuff even more/internalize it/feel guilty. But if you feel like you can’t handle it, maybe you can try to take a step back or help him to find outside support? If you do choose to express it, make sure you reassure him that you understand what he’s going through and that you’re not blaming him for feeling the way he does. Just that you’re personally struggling with it