It seems that you have already done quite a lot- offering to listen, give him feedback, do house work, etc.
If you believe that there may be something that you could assist him in his business ex book keeping, interviewing, administrative duties, etc. see if he would be willing to give you some responsibilities. It sounds like he brings the stress from work to the home. IF he is active any physical work out/exercise would be helpful to reduce some of that as well as meditation, doing things as a couple even if it is taking walks in the neighborhood. Sometimes doing things versus talking may offer a different outlet to solving an issue. See if there things you can do to reconnect emotionally with him (whatever had worked in the past, be spontaneous and patient.)