This is just an arranged marriage. Neither of you wanted this, especially him. It was too early, Sirius wanted his freedom, not being stuck with someone. But its all just for the sake of both families, or that's what his parents repeated over and over again..if this is just fake, why did he feel so bad when he made fun of you? When he just spitted insults for no reason.. why did he feel bad when he said "You're nothing to me."? And did he really need to cheat?