Answer:
Elinor and Marianne are surprised and heartbroken by Willoughby's engagement. Willoughby had given Marianne affection and given her intentions of a possible engagement with her. To them, it came as a shock, and none of them expected it at all. Others were watching Marianne and Willoughby, and they assumed that they were too crazy for each other. They seemed to spend every hour together.
Sometimes the ones that we trust the most, can be dishonest. We sometimes expect good things in life but we don't always get what we want. Love can be one-sided without us realizing it. Life isn't fair and it isn't perfect. We got to do our best to succeed in life. Things don't come to you on a silver platter, it's not that easy. You can live with someone for years and still not know about them and know how they feel. You can spend a small amount of time with someone and end up creating an everlasting connection. People try to change themselves or someone else, but it isn't that easy. If you love that person then you wouldn't try to change them.