What is wrong with my son?

My 15 year old son loves to listen to music on his iPod. But, this afternoon...I overheard my son singing Justin Bieber's song 'Baby'. Is this normal? And, last week, I also saw a text on his phone that said, 'I had so much fun last night! I hope we can do it again soon ;)' from someone named Kevin. Who is this Kevin? What does this mean? My son tells me that there is nothing wrong! I don't know what to do *starts sobbing*...It's just so heartbreaking!