Dean always thought "normal" was unachievable if you were a Winchester. His whole life had been far from anything close to normal, but that had never bothered him. Normal was for losers and people who were unaware of the truth- what was really out there. He could never imagine a life not fighting demons or any other evil s. for that matter. When Sammy left for Stanford he couldn't understand why he'd even wanted to go in the first place.
That was then, everything had changed since then. Dean was no longer a hunter or the man he used to be. Now Dean was the image of normality- living with Lisa and Ben, in a Chicago suburb, working a 9 to 5, 5 days a week. What the life lacked in thrill it made up for in different ways. Dean had become a father of sorts to Ben and found love with Lisa which combined made them into a little makeshift family.
It was hard though, to keep up the pretence because although Dean loved his new life he couldn't forget his old one. A lifetime of demon hunting does tend to leave some scars- both physically and emotionally. Sometimes he felt his old life got in the way of his new one, like he couldn't enjoy it for thinking of the past. Grief also held him back, the pain of losing his brother often drove him to find solace at the bottom of a bottle.
But no matter how much he missed Sam he had to go on, he promised he would. Dean promised he would be the best dad for Ben and enjoyed taking on his newfound role. Ben looked up to Dean and had the same sense of humour to boot-before long they were inseparable. After all the fighting and loss he'd endured it was nice for Dean to have his own piece of normality.