Anecdote: I had an IUD placed. It slipped and I got pregnant anyway.
Life is life and s*&^ happens, despite best efforts. It's how you deal with it that matters.
You have sympathy for her because she's a human being and someone you love. You don't have to like or agree with the things she's done, but you do have to try to see it from her perspective. If you want to be with her, you need to love her anyway and forgive. It only hurts you if you can't get there.
ME: 38 BF: 40 T: 10y, no kids, no M (by choice) BD: 7/14/14, BF admits to PA, wants out, lies about new R. 10/1/14: I move out, BF lies about move in with OW 12/4/14: OW confronted, reveals all the lies