OK, yes, it’s definitely icky for first cousins to get married (not to mention illegal in many states), but we kind of wish that we could rig up some kind of alternate universe portal and just see what would happen if a healthy, vibrant, and very much alive Ralph encountered Isabel. This healthy Ralph would be a really, terrifically awesome guy – smart, funny, caring, and incredibly sensitive. We don’t even know him, but we miss healthy Ralph. We wish healthy Ralph were present in the novel, for his sake and for Isabel’s, not to mention ours.
However, no such magic portal exists, and the Ralph Touchett we know and love is certainly far from healthy. His awareness of his own mortality prevents him from living life fully, even though he suspects that he’d have a great talent for it. Ralph’s illness provides him with an excuse for his indolence and his somewhat cynical, distanced approach to the rest of the world. The only person who can get under this shell of indifference is his cousin, Isabel, the light of his life. Their love is one of the most touching and important relationships in the entire novel, and we suspect that it’s what keeps him alive for so long.
Ralph is both one of the most and least perceptive characters in the book – that is to say, he sees everyone clearly but Isabel. His love and admiration for her make him invest too much confidence in her choices; he longs to live vicariously through his strong, vibrant cousin, and it’s possible that this desire to see her really live blinds him to the mistakes she’s capable of making until it’s too late.