"Well, I was just...Connor and I...we had a really great time this one day recently."
"Evan was having some trouble in terms of... the financial burdens of college. Larry and I started thinking about it, and we were very fortunate..."
I don't want Evan to get the idea that it's ok to rely on other people for favors.
With a practically "bored" mother, to a caring father. The Murphy family represented everything he thought his lacked, because Evan never got to have a father son bond, which also was the reason his mother was so busy. It didn't make it any easier that Evan was in a way the puzzle piece for each one of their broken relationships with Connor as well, and fit the role of savior for Cynthia and son for Larry.
Not just lovingly but financially the murphys want to take care of Evan, and his college expenses because of how much he has helped them get over Connor in their rough times. Heidi take this as an insult and creates the point of most tension between Heidi and Evan. This causes Evan to practically treat the Murphys as his family until he tells the truth at the end.
Even though Zoe wasn't part of Evan's "Picture Perfect Family" as a sister, but as a significant other; Evan found his newfound relationship with Zoe the perfect situation. This completed his fantasy of the better life that he craved.