Derek had been tempted from the day he arrived in the past to search out his family. The people he had loved before the world ended and life became a living nightmare. Somehow he managed to suppress his desires. The mission was too important. They had been sent back for a reason and he couldn't let anything come between him and his mission. Stopping Skynet, stopping Judgement Day was all he could allow himself to care about. Nothing else mattered.
Of course, that changed when he met Sarah and John Connor. He didn't forget about the mission. That would be impossible. However, he found his priorities shifting slightly. He had failed to protect the men in his unit who had travelled back in time with him. Part of him knew that it was because they were all so focused on their own tasks and their own theories of how to stop Skynet once and for all. They were so busy focusing on the details that they stopped looking at the bigger picture and stopped looking out for each other. They had lost track of exactly what it was they were fighting for. He had already lost too many friends for that to happen again. Somehow he had survived the attack on their safe house. It was just sheer luck that he had not been there with the others but, now that he was living to fight another day, he had to make each day count. He had to make sure that the mission of stopping Skynet and changing the future continued but he also had to make sure that his day to day mission of keeping them alive was also maintained. John Connor had to survive because if Judgement Day couldn't be stopped, if they couldn't stop the robots from taking over and John was not here, there would be no future for anyone.
It was so strange to think that he had known John for so long and yet, in this time, he had met him mere weeks before. How was he supposed to treat this teenager who tried to act so tough but was so vulnerable? How was he supposed to reconcile the young man with the memories he had of the leader of the Resistance? Already he could see traces of the man that John would become. He could see traces of the man that would become his friend, the man he would follow blindly into battle, the man who sent his brother away on a secret mission never to be seen again. The longer he stayed with them , the more he could see. The more he watched John, the more he saw the past staring up at him. In time, it wasn't the John Connor he knew from his time that he saw. When ever he looked at the teenager, he was staring straight into the eyes of his brother. The brother he knew he would never see again.
Derek didn't know exactly what had happened but the way his brother had disappeared had been fast and secret. When the bombs dropped, their parents had both been killed. As the world woke up to the apocalypse and the war started, he had taken their place. He had become Kyle's only protector in a world gone insane. As Derek trained and became a soldier, he in turn trained Kyle. He kept him safe and taught him how to survive until he was old enough for them to fight side by side. When Kyle was gone he screamed and shouted, rallied against John's leadership for the first time, desperate to know what fate Kyle had met. It was the only time that John had refused to share his plan. At the time, Derek had thought that John's refusal to meet his eye when he demanded an explanation was proof that John knew he was in the wrong. Now, he knew different. Now he knew that John had done the only thing he could. John had sent Kyle back, knowing that he would die but also knowing that if he didn't he would never be born.
Some people might argue that John didn't know who his father was, that it was all just fate, but Derek knew different. It was in their tone of voice, the way they said his name. Neither Sarah or John could mention Kyle without betraying their emotions. If it was him that had to send Kyle back, would have been able to do it? Derek knew that he wouldn't have, despite the consequences. He had loved his brother too much. In the future, had John loved Kyle? Who knew? As far as Derek could remember, John had never treated his brother any different from the rest of them. Apart from his good luck photo, of course.
Suppose John had decided not to keep his secret. Suppose he had proclaimed Kyle, a boy 16 years his junior, to be his father. Would John have become their fearless leader or would he have been considered to be crazy, driven insane by the machines? If the truth was known, would the machines have sent a terminator back in time to kill Kyle instead of sending one after Sarah? Time travel made everything complicated, so much so that you couldn't think about all of the 'what ifs'. It was hard enough trying to keep your own timeline straight in your head. All you could do was live one day at a time and hope that whatever changes you made to the future would be a change for the better.
It was hope that kept Derek going, both in the tunnels beneath the scorched earth for the future and here in the past. As he sat with John in the park, hope was all he would allow himself to feel. He didn't know what John was feeling or thinking as they watched a younger version of himself teaching Kyle how to swing a baseball bat. How could he possibly know what it felt like to watch your own father as a child? All Derek knew was what it felt like to get one more glimpse of a brother he thought he had lost for ever. All he knew was that seeing Kyle as a child, in the sunshine and having fun, was the best thing that he had seen in a long time. It reminded him that there was a time when Kyle was happy and innocent. It gave him hope that, no matter how much he lost in reaching his goal, the mission would be achieved. The future, the past, it didn't matter. Derek was exactly where he was supposed to be. If there really was no fate but that which we make for ourselves, then accepting the mission to come back in time, to stop the war against skynet before it began, was exactly what Derek needed to do. He would go on fighting as long and as hard as he could to make sure that Kyle could stay free and young and innocent for as long as possible. He knew what he was fighting for and nothing else mattered.
A/N - thanks for reading. Hope you enjoyed my little fic and didn't find it too rambling.