The function of oxytocin is far more complex than this. Oxytocin does play a part in pair bonding, but it is involved in many other things and cannot be thought of as a ‘love molecule’. We know, for example, that it can also enhance feelings such as jealousy and schadenfreude (taking pleasure in other people’s misfortunes).
Kemp AH. The role of oxytocin in human affect: a novel hypothesis (PDF). Curr Dir Pyschol Sci 2011;20(4):222-31.