Your "reactivity" to this new challenging time in you life is familiar. I was there too, it's pretty normal reaction to the new stressors in your life. I found mindfulness meditation was a game changer for me. It helps calm the waters and acknowledge, but let go, of the reactivity you are experiencing. Your are right to understand your tone affects your husband, the meditation will help you take a moment to breathe, reflect and choose how you respond to him. An additional option would be a support group where you would get support, some are available thru the Alzheimer's Association both in person and on line.