Hi, I'd like to help you with your question.
Has your husband seen his doctor yet? Sometimes, as men get older, their hormones change and their moods are affected. This can cause depression, anger and other issues. The fact that he acts better around his friends is a bit telling, but you cannot be sure unless the doctor examines him and determines if there is a physical reason he is acting this way in your marriage.
It sounds like you have tried what you could to help your marriage improve. If your husband is not interested in making things better, it is going to be very difficult for you to work on the marriage by yourself.
There are a couple of things you could try. One, you could attend counseling yourself. This would give you time to sort out what to do and give you someone neutral to help you decide how to handle your marriage. Two, you can work towards a separation. I understand you have the stress of your mother's care, so start slowly. Decide how you want to support yourself if you would leave, then work towards that goal. Maybe you need a certificate, or an associates degree to get the job you want. Or you can volunteer to work your way into a job. Look around for a place to live if you intend on being the one to move out. Just get a general idea of what it would take to be on your own. Then decide if it is worth it to you.
Are there any aging services for your mother? If you have not already, contact your local area agency on aging and see if there is any help they can provide to you with your mother's care. It would lift some of the burden and give you a chance to work towards dealing with your marriage issues.
Here are some books that may help you decide what to do:
Should I Stay Or Go? : How Controlled Separation (CS) Can Save Your Marriage by Lee Raffel
Too Good to Leave, Too Bad to Stay: A Step-by-Step Guide to Help You Decide Whether to Stay In or Get Out of Your Relationship by Mira Kirshenbaum
How to Know If It's Time to Go: A 10-Step Reality Test for Your Marriage by Dr. Lawrence Birnbach and Dr. Beverly Hyman
Most of all, remember to care for yourself through this difficult time. Spend time with supportive people in your life. Talk to others about how you feel, and get some "me" time every week so you do not become run down.
I hope this helped you,