I actually had to write a paper on the book for my world lit class. I think he was in love with her. It is a complex story for sure. I haven't seen the movie.
well i think it had to do with his upbringing as well as his relationship with winslet's character. from the beginning it is clear that he led a very sheltered existance. his first relationship where he actually opened himself up, just vanished without a trace. that kind of ordeal can make someone very gaurded emotionally. that is probably what led to him not being able to have lasting relationships with women, he just couldn't allow them to get that close to him, he'd be too vulnerable. but hey thats just my take. he obviously had relationships with other women, he got married, but i dont think he could really give them what they needed/ expected from him.