Although he’s lately become more of a popular guy (he dated an actress!), Dan has definite nerd roots. We are talking about the only Gossip Girl character seen studying on a regular basis. Also, he writes poetry. Only a nerd would do that.
Serena van der Woodsen slept with Nate Archibald. Upon returning to New York, she dated Dan. That went on for a while. Eventually, she went back to Nate. But Dan Humphrey wanted her too. So they told her she had to choose. She did.