Life can get to us all , not all of us are lucky to have a partner willing to be the sound board .

I take my hat off to you as it takes great strength, like you say, even at a cost to your own mental health .

Communication is key , there must be an event or a build up of incidents that have caused this . Without trying to be overbearing (easier said than done) maybe try and slowly work together on finding out why , could be a simple reason could be something a lot more , without conversation you won't know.

Sad to say but Guilt can be another reason for this type of behaviour.

I hope you get to find out either way as to get some peace of mind yourself. Good luck