My father and mother have lived with me and my family for 20 years and it has been a good, close relationship. My father is struggling and getting more depressed and we're not sure what more we can do. Together with our siblings, we arrange to bring him to visit Mom several times a week and also take him on other outings. He appreciates it but his heart is broken and I'm constantly worrying about him. I don't know how to free myself of the worry and guilt
You might also encourage him to see his doctor and maybe they can give him a mild antidepressent to help him cope.
Know you are doing your best and it is appreciated; but unfortunately you can't fill this huge loss for him. He now faces being separated from his life partner, losing her bit by bit as she slowly loses their "together" memories of people, places, events, and trying to come to grips with their mortality and grieving the huge loss of "what used to be" that he can't get back.
You and your sibs sound like wonderful, caring human beings, your parents are blessed. Be patient and realize "you can't fix it" (I know you want to!).
Hugs to you and your dear family.
Personally, I think when very sad events occur we are entitled to feel very sad. It is not at all unusual for family of persons with dementia to go through some mourning along the way, as well as after the loved one's death.
That is why I ask how long ago Mom went into the NH. If this continues indefinitely and/or it gets worse, maybe some counseling or a doctor's visit would be helpful. Otherwise, the things that you are doing sound very appropriate. Give Dad time to work through his feelings. Be gentle with him. Don't make him feel like there is something wrong with him.
As for your own feelings of worry and guilt, could some of your distress be your own mourning for the mother you used to have? It is OK to feel sad.
As for the guilt feelings, that pretty much goes with caregiving. There are so many questions and no obvious right answers that we are constantly worried that we've made some "wrong" decisions. Sigh. Live with it, but try to push it to the background.
Your mother has a horrid progressive disease. This is Not Your Fault.
Your mother's disease has progressed to the point where she needs and deserves care in a professional setting. This is Not Your Fault.
You father is understandably devastated by your mother's disease and its recent progression. This is Not Your Fault.
Emotionally the guilt is hard to shake. But at least know rationally that you've done nothing to feel guilty about. You are doing your best, and it sounds like that is very good indeed.