Edit: although I guess looking back again, the ex is blushing so maybe it will be a hopeful end, but still kind of a douchey thing to do to not let them know you are there beforehand and to make her feel bad when she gets back.
Seeing how the petals are being colored again at the very end, I'd say it implies a happy end, yes.
I don't think its sword whoever puts the barrier trying to protect maybe its the shrine itself, maybe its a place for a ritual or something.
I doubt it's just a place. You don't need a barrier like that to protect a small and rather inconspicuous shrine no one really takes notice of anyway if it's only that. There might be something (or someone) else hidden in the shrine.
I'm looking for manga that about two women on boat. They are age gap and married x high school. They were "running away" to be together. Please help me to looking for it ^-^