Two more quick things:  
1) The hardest person I ever had to love was my drug addict niece.  It required me to walk away from her;  completely the opposite of my "be nice" instinct.

2)  Many more marriages would last a lifetime if people understood love as a command not a feeling.  But to become a recipient of love requires making your desires known rather than silently fuming. (That's what causes people to seek affection outside of the marriage).  You have to communicate:  Jesus said "What do you want?"