I know the guilt you are feeling, I lost one of my shepherds and my first bengal cat to cancer. Like Alpha I opted not to go with chemo and lost the shepherd five weeks after she was diagnosed. Pancreatitis is a terrible illness, my sister had a shepherd much like your case where it kept flaring up and it got so bad she too had no other option but have him put down. As hard as it is we do what we have to do, we don't want them to suffer anymore and the guilt is a natural response to ending their suffering. You did the right thing, in time you'll come to realize that. Its the least we can do for them to let them go peacefully than to suffer an agonizing death. Peace to you and your family at the loss of your girl. My sympathies are with you.
he is your friend and protector, he will love you unconditionally, you owe it to him to be worthy of such devotion