So sorry you and your DH are going through this at such a young age. I am on the other side, the person with cancer with 2 kids but was 48 when diagnosed.
Emotionally its very difficult and a rollercoaster. Be honest with your husband about how you are feeling and let him tell you how he is feeling and you can support each other. Its actually easier for me when my husband is honest than when he is positive, when he is positive I feel very alone as there is pressure to be positive too when you are feeling fear. The approach I like best is simply when people ask me how I am feeling, let me be honest, and support me whatever and just let me know they are there for me no matter what and will support me in whatever choices I make. The best people I have found for this are others with cancer as they get it, they know to ask how each appointment went, they know to ask how I am and that some days and some treatments will be awful, they understand some days I will be depressed and some days I will be terrified. There is no pressure to pretend everything is fine and easy, often you can only offer sympathy to each other but having each other there means so much.
When things are really bad the best thing is to take things day by day or treatment by treatment. Just focus on getting through that day, its more manageable. Find people in similar situations and keep in touch, that is the best support. Counselling can help, Macmillan does cancer patients and I found the best emergency one for reliability is the Samaritans, they don't know much about cancer but just knowing someone has volunteered their time means a lot even if they say the wrong thing. I personally wanted to know the likely outcome and all the best treatment options so I did research and it helped me and talking to oncologist, can be very busy in hospitals at the moment and I have had nowhere near the time I would have liked. But through discussing with others with cancer and researching before oncologist then asking them have got answers I need. Macmillan do have nurses as well who can answer cancer questions and I would also consider if you have the funds talking to a private oncologist / surgeon as needed. Though I find others with the same cancer can often answer a lot of the practical questions like exactly what happens in surgery and after or on chemo, I found it useful to follow people ahead of me in treatment and in turn I help those behind.
As to outcomes it becomes clearer as you go along what the likely outcome is but certainly with my cancer there is a 30% chance it could come back at stage 4 at any point and then average life expectancy is around 3 years so the threat of that is always hanging over you and its a lifelong risk. Its hard to deal with that and you do grieve for the carefree life you had before and the life you thought you would have that has been taken from you. But I try not to dwell on that as that is taking the life you do have away. I think I am grateful for the 48 carefree years I had pre this and if I had been born 100 years ago would be all I got anyway. I try to enjoy time when we can, its difficult on chemotherapy now but any break you can get take it and enjoy it and forget about cancer for then, I pretend its not happening to me and distract when I can, TV, music, anything you enjoy. Do things you have always wanted to do, don't wait for later, as you don't know if that later will come. I went to Edinburgh in Feb and then Skomer to see puffins at Easter in treatment when having breaks. There are charities which can help provide breaks as well. If you can't get away even the days out you can get will help. Exercise also helps, 20 mins a day and I read that 3 to 5 hours a week reduces risk of reoccurrence 50% I think so definitely worth being active when you both can, it is also good for mental health doing 20 mins a day. It can be the last thing you feel like but push through if you can. It does not need to be very energetic, can be 20 mins stretching legs, arms in bed or a walk but something.
Take time to make sure you are OK as well as its hard as the caregiver. I have also done practical things like a will and preparing for if I die, its depressing but then you know you have done all you can if the worst happens. I also found pets really helpful though they are extra work, am getting a Maine Coon next month always wanted one and its lovely when the kids are so excited about it as its tough on them. If you have kids tell the schools so hopefully they will put support in place and advice is to tell kids but its best when you know details of treatments etc as kids ask questions.