Researchers of the University of North Carolina have found out, that romance is linked to depression. Especially young girls who are dating someone show increased depression levels.
As married people have happier lives than unmarried people the result was surprising.
Possibly teenage girls are not settled enough. They make their lives too dependent on this one friend so that little arguments get them very depressed
But it's not clear if it's only romance and little self esteem that causes the depressions.
Possibly only teenagers who have lots of arguments with their parents (and therefore are unhappier) are more likely to date someone.