Dandy speaks the truth. My STBXAH and I were long distance. We also saw each other every other weekend, and each trip involved a 1,000 mile round trip drive by one of us. That totally makes it impossible to really get an idea of what the other person really like on a daily basis. Everybody still puts on their "courting face" when you only see each other for two out of every 14 days.
I don't think anybody is saying that you're feelings weren't real, and that you didn't work on things to form a lasting relationship. All we are really trying to say is that for virtually all of us, our relationships started in the same way, and that generally speaking, those ultra intense feelings right at the outset are often a red flag for something unhealthy percolating under the surface in one or both people.