You and Eren are that couple, when Eren was 15 years old he always acted sweet to you not only that he also always protected you even always there for you, but when he turned 19 years old where he already knew the truth of the world, he was cold and grumpy to you because he wants to protect you, he doesn't want you to end up hurting when you know he's going to die, you can't marry him but Eren hopes you have to marry Armin..because Eren knows it's best