the blonde smiled at peggy now, he was happy to be back in her presence and know she was safe after she risked her life and howard as well to fly the captain into enemy territory.
"i do appreciate it, and i do yeah, jamie is my best friend, we grew up together and she always protected me. i had to save jamie." steve was known to get sick before the serum alot or end up in fights, and jamie would always protect him. this was steve's way of returning the favour, keeping the promise, 'till the end of the line'.