i was summer (only less attractive)

I went and saw a movie tonight. My mom and I are frequent patrons of the late night movie, and it is one of my favorite things to do. Put kids to bed and meet and the theater. I almost always leave satisfied with our choice of movie. Last week it was "Julie and Julia." Loved. Tonight we saw "(500) Days of Summer." Pretty much everyone I've talked to has raved about it and promised a delightful story with good acting and compelling music. 

Why did I leave the theater tonight feeling sad? (If you haven't seen the movie and plan to, stop reading because I'm about to talk about the ending.)

I can't shake the melancholy off, and I am worried that I know why. It's because I was Summer, isn't it? I was the girl who had someone's heart and I broke it. I wasn't dishonest (quite the opposite-- we both knew what we were signing up for), but neither was Summer. Tom knew that she didn't want anything serious all along. I wasn't mean or intentionally hurtful. Neither was Summer. But oh! The pain that she caused! Tonight the pain that I must've caused is feeling more acute, perhaps it has been ripened with time and a more mature heart. Of course in the end we all have ended up with who we were meant to be with. She is so much better with him than I would have been, and I have no doubt that my husband is my perfect match. Why do I feel so bad then? I hate knowing that I hurt someone, even though I know he is grateful and happy (now) that I did. Is that weird? Is this familiar to anyone else, or am I a little crazy? Maybe I have some apologies left to say? Not sure.