You've been dating Bellamy for a years now, ever since you landed on earth with the other 99 teens... You and Bellamy had your ups and downs in your relationship but deep down he knew you didnt love him, at least not anymore he knew that you were in love with someone else

And he knew that the one you loved was his sister, Octavia, not you.... You never told him but he knew it, he could understand it, he could see it in the way you looked at her, the way you risked your life every time just for her, the fact that you always worried about her more than you worried about him. It was clear you were in love with Octavia and he knew he couldnt keep you anymore

After Clarke killed A.L.I.E. and found out about Pramfaya, a nuclear apocalypse that will take place in a few months... You were all trying to find a solution to save the world... During the black rain, when you all ran inside, Octavia didnt make it on time and was left to burn. Bellamy went to dress up quickly to go rescue his sister but you were quicker and without anything on your ran into the burning rain to save Octavia.... Bellamy gasped, by your action to risk everything for her, he knew he had to break it off