Colon cancer metastasized to lungs: Husband severely depressed

hi all. Haven't been here for a while, although have been thinking about coming back. My husband was diagnosed with colon cancer 6 1/2 years ago. His cancer metastasized to both of his lungs 3 years into this nightmare. He has been on every treatment program for colon cancer, all the chemos, and immunotherapy. He is on a chemo with an immunotherapy treatment right now. Dr did the test and found out he has the wild kras gene.
I'm not sure I am saying all this correctly. Because I feel like I've been in a whirlwind totally helpless. He had a PET scan yesterday dr told us the treatment plan is working. still ! He will have 6 more treatments then another PET scan. If it is good they will do a lung biopsy and take out the biggest one. My question is any other caregivers dealing with the patient being severely depressed? It's getting worse. Sometimes He's like jekyll and hyde! Is this normal side effects?