When things are going good, it’s not difficult to love your mate. Your real love shows off when things are going down. When the other person is going through a bad phase of life, she cannot be as nice to you as she used to be. If you are always driven by “the law of reciprocity”, instead of supporting her, you’ll make the situation worse for her.
However, it is not difficult to think that when she is not so nice to you, probably that is the time when she needs your love the most. How you behave in those times will determine whether you can be called a real “lover”. A person who behaves nicely only when he is behaved with nicely is not a lover, as Gurbani says, he is just engaging in selfish transactional behavior.
The same is true in spiritual life w.r.t. love of God. If we love God only when things are going our way and doubt or even curse God when things are not going our way, we are not lovers; we are transacting with God for our selfish ends.