If a person divorce, it can get it over with their first marriage and then have a second love story and a second marriage forgetting easily the first story.
But in the case of an untimely death that split the couple, the remaining one will never say goodbye definitively to the first person...because it technically didn’t happened, probably; so they can try to move on, find a new love and really mean it...but there will still be that “lingering feeling” about the first husband/wife.
Often the new partner knows about it too (and if they are “human inside” they’ll understand).
@Rhino126 If you are referencing the part where she is standing on the beach next to somebody, I think that other person is the same one who wrote the letter. Despite what the guy wrote in the letter, she did, as you said, acknowledge the fact that she still loves him, while standing seemingly on the same beach as in the past. Otherwise I think it would be weird to come and declare your love to your previous s/o in a place that seemed special in a new relationship but idk lol could also be the other way