Syl is a self-centred jerk, alright. I bet he's expecting Octavia to be oh-so-convenient. So while he's off extolling having found his "true love" and indulging in a biologically fruitless relationship when he needs an heir, he'll shovel his little sister into a political marriage and make her go through the life-threatening process of pregnancy and childbirth more times than which ever household she is married into requires for its own heirs. If I've understood the setting correctly, the setting is medically equivalent to the 1700's – 1800's, when death from complications during the reproductive process was the leading cause of death in women of child-baring age. Not that they were very likely to die, but that it was less uncommon. So if it isn't out of necessity or love, that is an extremely selfish thing to ask, let alone expect.
Question: This particular BL universe does not allow polygamy or GL? From a practical stand point, isn't that going to cause a lot of issues?