Love or Duty

I often struggle with whether I am doing things out of duty or out of love.  Like "duty-bound" Aeneas, I find myself doing things that I don't really want to do, but I do them because I think it is the right thing to do.  But surely, that is not the attitude that the Lord wants from us.  We should serve Him out of love for Jesus and all He has done for us.  How to you love someone you haven't seen and cannot touch or hold?  Yet, I know that I love Him, for I feel it deep within my heart.  How do I change duty into love?  I haven't figured out the answer yet.