With the technology and internet, getting to know each other can be done even from far apart. If work and other obligations force a long distance relationship, with all these skype, facetime etc, it's easy to share your life and everyday activities with each other. I'm making a wild guess, that Meghan and Harry have spent tons of time getting to know each other this way.
IMO Meghan and Harry are both charming people, easy to like, easy to get on with. Both are intelligent, witty, caring etc. I'm making another wild guess, that they've completely charmed the pants off each other with their personalities too, not just physically.
My last wild guess is, that neither would settle for a relationship they don't want to be in, Meghan is with Harry in his home, because he wants her there, and she wants to be there. I don't think either one is the settling type, they have no reason to settle.