Platonic love
Two lonely souls carefully confine each other
"We can't be together all the time, or even meet rarely. If you are here, I don't care about the outcome."
Two-way redemption in the early stage and soul mate in the later stage
I'm not sure if they were truly happy in the end
But I am sure that no matter how many latitudes they span in time and space, they all know each other's inner souls and are irreplaceable.
Purpose: spiritual love