It is tough for me to accept too. I think it's easier in S&S because there is an actual engagement, a real promise that would be breached if Edward broke the engagement. Here Wentworth is going to sacrifice himself merely because he raised the expectation of marraige.

It is tough to relate to it but courtship was so totaly diffeent from what we have now in so many ways that I can't help but agree with your question, "Why doesn't it seem to occur to him that *she* might be better off married to someone who actually loves her?" And why can't he just be direct about it?