@monroeed- Good morning and welcome to Mayo Clinic Connect. It sounds like your boyfriend is doing well despite his discouraging news.I know just what you mean, not knowing what to say. Even after 22 years with lung cancer I still get a bit nervous when someone tells me that they have cancer (s). The most important thing is to be honest. One of the things that angered me a lot was when people would tell me that I was tough and this would be nothing for me; God will see you through this; my friend's cousin had the same thing and she didn't make it; there's a special cancer diet, There are good foods for you and those are the best. There really isn't any special diet.
Science based facts are necessary for me so that my hopes don't get high and then those facts turn out to be false.
He might be very confused, not knowing how is he going to get through all of this. Make sure that you reassure him that he isn't alone. You must love him a great deal to search for help. Ask him what he wants for conversations. And if he doesn't want to talk sometimes let him have his time. I feel that it's more important to learn what not to say than there is to say because your intimacy with this man will help guide you.
Last year I began a blog about my experience because I was so overwhelmed with having cancer. I needed an outlet! I hope that he will read this, and you. I deal with a lot of your questions.
https://my20yearscancer.com/
Here are some more links to help.
https://www.mayoclinic.org/diseases-conditions/cancer/in-depth/cancer-survivor/art-20045378
https://www.cancercare.org/blog/cancer-i-care-i-weighs-in-what-not-to-say-to-someone-who-has-cancer
Here is another link: https://connect.mayoclinic.org/group/kidney-conditions/

Please feel free to ask me anything. I will try and help guide you. There are many many conversations on Connect and reading those will help. Do you think that your boyfriend would be interested in joining Connect?
How have you helped him through his other cancers?