Frank McCourt's portrait of love and family is definitely a complicated one, and there's lots to say about it (more than I can put here!). I hope this is a start.
McCourt's family seems tied together by deep bonds of affection—but (as in most families) that doesn't always stop them from disagreeing, hurting each other, or giving way to anger, resentment, and jealousy. Frank is shocked to discover that his father's family blames his mother for his father's excessive drinking, and when his father (who abandoned the family when Frank was ten) visits again after many years, old tensions make reconciliation impossible. Frank also struggles with deep envy for his younger brother, who has followed him to the US and made good as he hasn't yet; Malachy, with his popular Manhattan bar, has won both money and fame. Yet together he, Malachy, and Michael all work together to support their mother, who eventually joins them in New York. Unfortunately she can't reconcile herself to her new life and pushes her sons away; her existence becomes a lonely one despite the best efforts of her children. If there's a lesson here, I think it's for all of us to find on our own—but at the very least we can appreciate emotions that (to some degree) are familiar to all of us, and admire the love that was more often than not strong enough to overcome it.
McCourt's descriptions of love and family are remarkably honest, especially those concerning his successes and failures with the family he starts. His relationship with his first wife, though always marked by ups and downs, begins to fall apart (a painful process he describes vividly and perhaps blames in part on his own drinking). His description of his reaction to the birth of his daughter is also painfully honest; Margaret is born with birthmarks on her feet that Frank initially finds disturbing, a violation of the perfection he hoped for. He recovers, however, and loves his daughter. By relating both the noble and the ignoble emotions and aspects of family and love, McCarthy tells a story that's powerful in its honesty.