Evan went through a big evolution from initial idea to who he is now. The original idea was for a classmate you'd occasionally see and could hook up with, and the name and personality were totally different. That version of the character wasn't meant to be seen anywhere except class/between classes.
When I couldn't get the character to look like I wanted, I messed around in Daz until I came up with Evan, and how he looked led to a personality change. I liked writing his and Connor's interactions so much that I wrote him into the party, and I went on to realize I wanted to keep writing more scenes with him.
So he's the only romance that wasn't preplanned and just happened organically—kind of like meeting someone unexpectedly in real life, I suppose!