So with the love for her and the thankfulness for her, is it strength I have to look after her? Or is it just normal human love.

Human selfishness is what is natural, what you are doing is supernatural. Pain management and care like this is no easy task and you seem to be handling it with great fortitude and strength. Taking vows seriously and fulfilling them, even when it is difficult, is what it really means to be a person of faith.