Long distance needs long visits
You can’t get a real feel for a relationship in infrequent three-day bursts. If the visits have always been short, that comes with the pressure of “Okay we need to get along because if we get in a fight that’ll ruin this very short trip and then we won’t see each other for a while!” Nobody is truly themselves under those conditions. You need long visits to see how compatible you really are. You need to see how you fare with the understanding that this person isn’t going anywhere any time soon.