Of course you miss him. If you didn't, I'd think that there was something wrong w/you and the relationship. You were together for quite a long time and now he's left this empty void. Your support system went out the window when he left...but there are others that can step up to the plate to support you right now. Lean on them.
It takes a long time to recover from thoracotomy/lung cancer. So, don't be so hard on yourself and keep your expectations of what you think that you should be doing or where you should be at this time to a minimum. Give your body time to heal.
As for your family and friends, until they walk a mile in your shoes, they don't have a clue as to what you are dealing w/when it comes to you and your h at this time. I would suggest that you select one or two close friends to talk to about your situation and leave the others in the dark unless they inquire. If they inquire, keep your responses short and sweet.
I'm glad you joined a support group. They will help you. You can always come here to vent, be angry and yes just seek old comfort from those who post here. The posters are on the same path w/you, but are at various stages along the way.
Try to keep the focus on you and getting better. Stress can play a huge role in healing.