Elderly father with chronic pain becoming hurtful in his words. I'm at a loss.

One of your comments stood out to me most, that he thinks seeking help is weak... however, there he is showing his issue of having no insight at all into how much HELP he is receiving from you. You are burned out, tired, feeling unappreciated and feel like you've lost your father. In a way, it seems to me you are already grieving the loss of your father. I think it's time to get some respite and support into place, if you can. As you say, you know things are only going to get worse.

It's good that you recognize the issues and a need for change. That should serve you both well. With this in mind, maybe, you can explore the options and come up with a plan for dad's care. If he's been in a chronic pain for a long time, I'd imagine that he is rather difficult to be around. I've experienced pain before and it really did a number on me. I have no idea how people live with it long term. And, I have a pretty high tolerance for it or so I've been told my a couple of dentists and doctors. Plus, your dad is likely still grieving the loss of his wife. It's a lot to deal with. Still, you deserve to live your own life and not be miserable. Do you have somewhere else to live?

One thing that did catch my attention in your post is that your dad has poor short term memory. Is this recent? I'd question if he might be having more than chronic pain and if his memory is suffering. That too, can affect how a senior behaves towards family members.

Family members' words can hurt us, but usually, we can overlook it, because we know that they don't mean it, are in pain, frustrated, etc. I'd try to figure out what's going on and then see if anything can help him, like medication adjustment, therapy, etc. If not, I'd explore other options for his care.

Your sadness and frustration come through in your post, I am so sorry that you have this situation. Putting your father's problems aside for a moment, I hope that you will focus on you. Examine your life, your health, and your goals.
This is not a dress rehearsal, as they say, and you owe it to yourself and your son (as well as the other people in your life who love you) to care for yourself.
Are you depressed? It certainly sounds like you have ample reason to be. But what can you do to help yourself?
Remember, you are an adult. Answering to where you are going or explaining your choices is playing into an unhealthy cycle leading to resentments. I support the idea of posting a schedule for someone who has memory issues. It is considerate to let him know on Tuesday at 1 pm you will be out, or whatever. But you need not provide details. Let errands be you catch all. When we overly explain ourselves it implies that the person to whom we are explaining has the right to interject his opinions. That causes problems for adult children even when the parent is not dealing with emotional/cognitive or other issues like your dad seem to be.
You are generous to live with your dad out of concern and love, remember that you will not be of help if your health and or psyche suffers and causes you to harbor hard feelings towards him.
Be sure to structure your days, join an exercise class, yoga or other outlets that get your body moving. Does the local library have a book club? Join it. Are you part of a Church? Volunteer there or at a food pantry. These activities may only take a couple hours a day but they can give you a whole new perspective on your life.
If you share your schedule with your dad and he criticises your activities, smile and say "well, I enjoy it" and change the subject. Your life choices are not up for debate.

As far as your father's issues, chronic pain absolutely changes people. Personalities suffer as do relationships. Are you able to go with him to his next doctor's appt? Could you discuss the possibilities for physical therapy as another option? Perhaps he has had physical therapy in the past, but it may help now with maintaining and developing strength which can alleviate pain. Also, if your father has chronic back pain, you could look into massage therapy. It has been shown to be as effective as opioid medication for some back pain patients. It also has the benefits of physical touch which the elderly miss out on and has been shown to release endorphins that help with pain control. This is not a sexual situation, massage therapy is a legit and respected therapy for people in pain, your dad may need reassurance if he is unfamiliar with that aspect of it. But a massage even 30 minutes twice a week could be a valuable investment and help his mind and body.
If he takes narcotics for chronic pain, he may be constipated. While we do get tolerant to some side effects of pain medication, unfortunately, constipation can be an on-going side effect that people suffer from for years. I would be sure that he is not constipated because the combo of pain and constipation can be unbearable and can affect behavior.
Lastly, maybe he needs an antidepressant added to his regimen. I hesitate to add another medication for someone over 70 who takes many meds, but his behavior can be an indication of major depression which is common in chronic pain sufferers.
I wish you the best, please consider putting yourself first and establish a routine that brings some sunlight to your days. Start 2018 with a new outlook.
Margaret

Thanks you guys, some good thoughts and understanding. As we have tried a lot of the things mentioned already and he is a stubborn one about going to the doctor, etc. one thing we haven't tried is massage therapy. I will look into that for him. Meanwhile, I am going to get some counseling to learn better how to cope - I cannot move out at this point, so I have to figure something else out.