How do Winston and Julia feel about each other, and why do they feel this way?

In my opinion, the two of them are not really in love with
one another.  Winston may be more in love than Julia, but they are really both just
using the other to fulfill a particular need.

Julia is just
using Winston because she hates the Party having control over her personal life.  She
just wants to have some fun and she does not really care all that much about whom she
has fun with.  All she really cares about is her own desires and about hurting the
Party.

Winston is looking for a bit more than that.  He
seems to truly want to have a relationship.  But it is not clear to me whether he really
wants a relationship for its own sake or because such things are forbidden.  He feels
that what the Party is doing is wrong and he wants to try to destroy the Party's power. 
I do not know how much he actually cares for Julia in particular and how much he is just
having the affair because it is a human relationship that he longs to
have.