Hi, first of all, like everyone else, I'm sorry your discovery has upset you.
My own discovery of this sort of relationship was an even closer one - between siblings. The family story is that the brother had been abroad, came home to be met by his parents and much younger sister, didn't realise she was his sister and fell in love. She seems to have felt the same, and they emigrated to Canada.
I have some doubts about the story, which is probably why I don't feel upset about it. Their mother went out to Canada too (aged 68 - brave woman!) and lived with them there. A census has her as mother of them both, which is why I am slightly doubtful, I would have thought they might have said they were husband and wife? But who knows what is true? It might all be perfectly innocent and ordinary!
Ann