Someone finds him

Before Robbie could find one of the girls, Xander finds him. Robbie was about to brush Xander off and continue to search for the girls, when the Key alerted him to hidden depths that were only hinted at during the show.

Xander was a **** to be reconned with in his own right. He was relentless when he thinks someone was after his friends. He had an intensity that backed down a master vampire. He was also inovative when it came to his fighting style. Heck, the guy used a rocket launcher to take out a demon, that made him a freaking genius compared to the other people on the show!

If Robbie ignores him now, it will come back and bite him in the ass later. Mind control was an option, but if he lost control he was screwed.

That left the third option, merger. This would also give him an easy in with the other girls. Also the fact that Xander seemed to attract sexy women and demons didn't hurt.

After the merger was complete, Robbie/Xander heard a rustling in the bushes, someone or something was coming.