From Day 1, my Husband (Rick) was intent on letting my son (Deuce) know that he is his step-father, mentor, father-figure and any number of things, but never a replacement for his father. We made up a nickname for Deuce to call him so that there was no pressure for him to pick a name. Calling him by his first name seemed disrespectful and "Uncle Rick" or "Mr. Rick" were out the question.
They have a good relationship. I let them forge their own path (but sometimes slip up and interject when I should just observe). They show their affection for each other by giving fist bumps. Rick sometimes throws an arm across his shoulder if they're talking a life talk or he's encouraging him about something. Rick treats him like a son. He reminds him that he knows he is not his dad, but he still wants the best for him.
Deuce is only 9 (and 1/4). The hope is that we never have to experience the "you ain't my daddy" period that many blended families go through. For now though, we are just enjoying each other, providing Deuce with opportunities that we didn't have and trying to give him the tools to be his best self.