Love can never be
smooth sailing.
Bad guys are pawns of karma USED to further Love's cosmic
lessons.
I believe the existence of 'bad' guys (and woman) is paramount. If
Love was perfect - we will never, in our lifetime, discover the
true meaning of Love. Sure, we all know that Spring is awesome...
but have you seen Spring's ugly nature? Or the beautiful side of
Winter? Without bad guys, how do we know the 'goodness' of nice
guys?
There are reasons why certain people intrude into our lives. We,
acting as a security guard deployed at the main gate - deciding who
and who is allowed to enter. We form a relationship with those we
chose from freewill - nobody force a knife upon our throat to
accept those BGR.
In the end, we only have ourselves to be blame... the decision we
made. 
Cheers