Sick loved one giving up on life. What do we do?

I think your bf's dad is "giving up" because the medical system seems to have given up on him.
The simplest thing I could recommend is that you share with him anything by Dr. Sherry Rogers. She is a lifesaver.

She will send out a packet of free newsletters packed with information (almost all text, -- little space wasted on pretty graphics and pictures) on how to literally reverse and cure thngs like heart disease and cancer.
She does not claim to be anybody special. Just a doc who does her job and actually keeps up with the science -- and mantains her independence.
A second alternative voice that can bring hope, as well as useful information, is my doctor in the Chicago area. This is a recent one that is very pertinent to your dad's problems and covers solutions. His show is high-energy and obviously it aims to get patients into his practice, but beyond that, is highly educational.

Listening to him will help confirm that you're not crazy if you suspect something is really, really wrong with establishment medicine and its frequent lack of answers and frequent failure to adhere to known best practices. 
Best to all of you.

If he has had cancer, he may believe it's returned. Not a particularly good thing. He's the boss, applesauce. It's his call to make. Support him and you and boyfriend try to put it out of your minds. Enjoy what is.

If you believe he's an unsafe driver, go to or call his local police station and ask what you might be able to do. Every state is different.

If your boyfreind and dad are truly enjoying eachother company than it's okay..... Don't fight him.

Take away the keys, hide them. Have the doctor tell him he is unfit to drive, and dangerous. DMV will deny is license. It happened with my aunt. No more driving. let him live his life out the rest of the way. He has done so all these years. Just because he decided to make connection with his son recently won't make him get healthier. Perhaps he just wanted tie up loose ends. He is doing this...Better late than never... Your boyfriend should be happy about this. Spend quality time, not quantity time. MOvie night at his house, story time..Time to forgive and appreciate NOW.

If he is still mentally competent you can't force him to get care or go to a hospital. If it gets bad you may have to call 911 get him to the er for help. But if he refuses to be admitted or cooperate I don't think he can be forced. Does he have any medical directives like DNR?