As pathetically inadequate as my words seem, I wish you and the families affected all of my condolences and the best of luck going forward. As much as I am not a religious person, your story clearly demonstrates the beautiful side of religion that gets swept under the rug.
I'm sure you know this already, but give her time to heal. She needs to mourn and come to terms with the loss of her boyfriend before she can love again. Wait until she stops looking for him, and starts looking for love. No matter what, no one will ever be able to replace him, and she needs to accept this. Nothing would hurt more than being a "replacement". If she does love you, she'll love you for your kindness, your selflessness, your thoughtfulness, for being there for her when she needed a shoulder to cry on, for putting her before your own needs, for putting her feelings before your own desires, for who you are, not who he was.
I wish you all the best. Do what you feel you must. We will all be behind you. Always. ❤