Clarke didn't want to leave them all behind – but she had no other choice. Looking at all the faces of the people she had saved, it just reminded her of what she had to do – what she was forced to do – in order to keep them alive and safe. Bellamy had pulled the lever too, she knows that, but Clarke had shouldered the responsibility alone- she didn't want anyone else to feel the way she did or to feel responsible for killing all the people at Mount Weather. Clarke knew her people would miss her – try to find her even – but she knew that they would understand why she has to leave, why she has to go alone. She felt bad that she didn't get to say goodbye to her mum or to any of her friends, only Bellamy, and that she was essentially passing all the responsibility of keeping her people alive onto everyone else. Clarke wondered if it was a selfish act – that she got to walk away from the camp while everyone else that was at Mount Weather had to stay to pick up the pieces. But again – she had to leave, she had no choice. She knew her people would survive this, that they would all come together and help each other in order to survive, especially with her mum and Kane in charge of the camp.
Clarke wished it hadn't been like this, that Lexa hadn't made a selfish deal to only save her own people and forget about hers – but it was only wishful thinking and Clarke hated thinking about what ifs, they were too useless for her taste and she would much rather deal with reality. Clarke's own reality now consisting of walking through the forest with no real destination in mind, only wanting to get as far away from Camp Jaha as she could manage. She thought about finding Lexa, to scream and rant and maybe even kill her in revenge for her betrayal, but she knew it was too reckless – that it could potentially put her people's lives at risk if she even attempted to kill Lexa. So Clarke just continued walking, deep in her own thoughts about Mount Weather and Lexa and how those on the Ark would be able to adapt to this new world – she hoped that they would be able to come to understand Earth like they did, that they could understand why peace was always the better option instead of killing, but she wouldn't hold her breath for it – after all, when they had first come to the ground, they only person optimistic enough to hope for peace between the grounders was Finn and that meeting had gone horribly.
She had no idea what she was doing, she never really has, but she had always felt responsible and had tried her best to keep everyone alive. When they had first come to Earth, she was only 17 and she had no clue how any of them were going to survive living together much less the grounders. Clarke began to miss the early days, before Mount Weather, when the drop ship had been their home and before Abby or Kane had resumed their chancellor duties when they didn't know what was really going on in the world around them. She missed when the responsibility was on Bellamy and hers' shoulders – the kids looked up to them, and felt inspired by Bellamy and together they were able to make the best decisions for the group – but now, they had no real say when it came to the big decisions and it felt wrong.
Clarke wanted to turn back, to go tell Bellamy that she was staying and that she was an idiot for ever thinking of actually leaving. But she wouldn't – she knew this was the right decision and that she was sticking to it. She couldn't stand to see the faces of all her people and even though they've gone through so much together, she hoped Bellamy wouldn't miss her much, that she would be a distant memory soon so that what happened at Mount Weather would also be a distant memory that could be easily forgotten over the passage of time. She cared about Bellamy- cared that he was safe and alive as any friend would and it worried her that he was so quick to kill if he thought people's lives were at risk – but she trusted him and knew that he would protect the people in Camp Jaha.
Clarke kept walking, for hours and hours until her feet were exhausted and she had no other choice but to lie down and rest – so she climbed up a tree and secured herself with a rope so she wouldn't be able to fall. Clarke didn't want any grounders to find her, or any of her own people so she knew she'd have to continue sleeping this way for a while until her people gave up searching for her. She knew her mum would send people to search, and she knew she'd have to do a good job at evading them every time they came looking for her – she wasn't going to be dragged back to camp because her own mother can't understand why she needs to be alone. Maybe it was selfish, but Clarke didn't care right at the moment – she only wanted to forget all the people she had killed, wanted to forget their faces and how scared they must have been when they realised that they were about to die and that there was nothing that they could do to save themselves. Clarke knew it was stupid to dwell on it over and over, but she couldn't help it – she couldn't help believing that this never would have happened if they hadn't been caught by the "Mountain Men" in the first place – that all the people in Mount Weather would still be alive if they had waited inside the drop ship until they knew it was safe to go outside.
As Clarke started to fall asleep, she noticed where she was – she was in a tree close to the car where Finn, Wells, and she had fled to in order to escape the poisonous gas that had killed Atom. When she realised, she wanted to scream and yell that this was the opposite of what she wanted – that she had walked away from Camp Jaha in order to forget the things that she had done and had to go through, not be reminded of them. Clark hated being reminded of Wells – how poorly she had treated him when she had blamed him for her father's death when he had had nothing to do with it – she had hated her best friend despite knowing he never would have done that to her and then he had died.
Many people had died when it was just them on the ground, with no one from the Ark being able to communicate with them. People wandered off all the time, people got lost, people got killed, and people died because they followed orders from Bellamy and her. Clarke knew she was being slightly irrational taking responsibility for each person's death but she couldn't help it – she had been in charge, along with Bellamy – to keep people alive and she had failed them on more than one occasion. Clarke wanted to save them all – but again, she hated to think about what ifs so she left that thought trail and focused on something better – Lexa.
Clarke wanted revenge for her people – they had all been betrayed when Lexa chose to free her people from Mount Weather and abandoned her people to die. She wanted Lexa to feel what she had felt when she had been betrayed by her – but Clarke knew that was ridiculous because, even if she hated to admit it and never would out loud, she might have done the same thing if their roles had been reversed and the offer had been made to her and Bellamy. So Clarke couldn't find it within herself to completely loathe Lexa, but she still hated her – for abandoning her after she made a promise. Clarke also hated herself for ever believing that she could trust Lexa with her own people's lives in the first place but she had had no other choice if she had wanted to breach Mount Weather and wage a war on the Mountain Men to get her people back. Clarke was just grateful that it had worked out in the end – bloody, and horrible – but her people were safe and alive and weren't trapped inside Mount Weather or being drilled into for their bone marrow.
So, whilst she started to fall asleep again, she decided that she would go see Lexa – but not to kill her - to strike another alliance with her so that she could keep her people safe once and for all from the grounders and other enemies in the land. She didn't know what the terms would be yet or how she could trust her to keep her end of the deal, but it was her best shot at being able to keep her people safe and be able to know that they are being protected without her having to be there at Camp Jaha in person.