The characters were destined to be on the island. No matter how many times they tried to leave or tried to separate from each other, forces guided them back together. No matter what happens, whether bomb or not, flash forward, sideways, any of it, in the end, the right people still wind up together. Their lives may take different paths, but no matter what, they find each other. It may be a chance encounter that brings them together “off” the island, but in nearly every case, the characters feel the connection almost immediately. And they just know. They just “see” what is supposed to be. The events are things that happened on the island, but even though the characters didn’t experience it in the reality in which they are currently living, they feel the impact of the visions when they touch, and they know right away that they are meant to be together. And in the end, maybe it takes death before the duo can be complete. But hopefully, we can get it done long before that.
Regarding Jack and Kate… even through the Sawyer debacle, Jack still loved Kate. No matter what kind of peril he faced, he was always looking out for Kate. Even in the finale… rocks were falling, the ground was shaking, and he was still trying to get her to safety, even at the risk of his own. In the end, Kate was ultimately there to take Jack’s hand and sit him down. Hopefully after all the turmoil, that made Jack feel safe.
Maybe you didn’t see it the same way, but to me, this episode showed that if two people are destined to be together (Jack/Kate, Desmond/Penny, Sayid/Shannon, Charlie/Claire, etc.) they ultimately will. They may face danger or threats along the way. There will be heartbreak and strife. You will root for them and be disappointed at times. They will feel lost when they are apart and at some points, may feel as though they will never even see each other again… never hear the other’s voice or feel his/her touch. Things may get darker than either one of them imagined. But no matter what, somehow, some way, they will wind up in each other’s arms. And it will be glorious when it finally happens.