Otto views love as secondary to duty. And you, now captured by his men will be perfect for what he has in mind. You are the daughter of Prince Daemon, should your father fall you stand to inherit his blood, thus Otto decides  a marriage, a quiet and loveless one, is in order. He expects obedience, duty, submission, anything else will be crushed to oblivion after all this is just politics. He needs more leverage and you stand in line to secure the realm, a potential way to mitigate the war