An: Based on a prompt I got on Tumblr.
Last Kiss
A last kiss can be known whether in breaking up or sickness but still sad. The unknown lass kiss is the most tragic. It could be anything for a simple goodbye kiss to a passionate kiss to an angry kiss. But it would tragically be the last one with neither partner knowing making it all the more tragic.
Sirius didn't know that this was their last kiss but if he did he would have tried harder to remember ever detail. He would remember that feel of James' lips crashing against his own, the feel of his fingers running through James' hair, the smell that was unique to James that was Qudditch, wood, and the outdoors, and the feeling of James' arms wrapped around him holding him close making him feel safe and loved. Sirius would remember it all but he didn't.
James did know this was the last kiss but if he did he would have prolonged it. He would have poured all his love for Sirius into it, showing Sirius that he did love him and always will. He would stay longer breathing in the smell of fuel, oil, and fire that was so Sirius. He would have stayed longer holding Sirius close and just enjoying his presence, lips pressed together and hands running through their hair. James would have made it longer than it was but he didn't.
Instead, it wasn't necessary a quick kiss but it wasn't long either. It was a good-by kiss with James going into hiding to keep his family safe and Sirius going out to protect them risking his life (then they should have known but they were young). It was an everything-will-be-ok kiss where they will see each other again. It was never suppose to be their last kiss; they both expected to survive the war (even if that was a stupid thing to think but they didn't want to think of the other alternative). They were suppose to see each other again.
Instead, Sirius was throw in Azkaban blamed for a crime he would never commit reliving his worse memories until the only clear memory of James was finding his dead body. James was dead not able to do anything to help the living forced to watch the horror his best friend, his lover being torture slowly losing himself wishing he could be there with him kissing him and holding him telling him that he was loved. Their last kiss was the most tragic kind of last kiss.