As the chaos started to unfold during their 6th year, Draco pushed everyone away including Theo. He buried himself in other witches, trying to distract himself from his task, and stayed away from his friends. Friends, relationships, lovers, all could be used against him by the Dark Lord, and it wasn’t a risk Draco was willing to take. The remaining three refused to give up and towards the end of the war Draco started to give in and lean on them for more support. There was nothing he could do anyway, all three would be branded the minute they graduated Hogwarts. Might as well stick together.