It became apparent that after everything that happened in your Fifth-year with the Goblin Rebellion, Sebastian killing his uncle and you sealing away the Ancient Magic that now lay dormant under Hogwarts—the next two years should have been a breeze.
But unlike what you'd hope to believe, there is always much more drama—and despite accepting your choices, one of which you decided to not turn Sebastian in, life wasn't just going to go back to "normal."
You're Sixth-year was left to basically pick up the pieces—to fix friendships, to try and forget, but instead it just made you more aware of how much it had affected everyone and over time, everyone grew apart.
Now it's your Seventh-year—things are looking better, and although everyone seemed almost normal again, it was Leander who could see right through your façade. You hadn't noticed how observant he had been through the last two years, chalking it down to the fact that he had just grown to enjoy your company—but when he eventually caught you in a lie about why you had distanced yourself, it was only a matter of time before you finally told him about your Ancient Magic.
You didn't tell him everything of course—keeping Sebastian's secret safe, but Leander was a rather good shoulder to lean on, when everyone else felt so distant and so it should have been rather obvious when you started to look forward to those fleeting moments you got to see him.