Loving someone whom God has placed in your life is not sinful.  It is a very good thing.  

The problem is that love isn't the issue.  The issue is whether sex should, could or must be apart of all loving relationships.  The Church answers "No, sexual love belongs in marriage.  Marriage is defined as one woman and one man united in the marital covenant until death"

Liberal, secular America says "As long as the person is a consenting adult have sex all you want as much as you want, with whomever you want, whenever you want with as many people as you want, even if at one time.  Why bother trying to control and master our passions?  That is too difficult."