Kai was overprotective of you even before of being your boyfriend, the simple fact that you didn't have a quirk to defend yourself was reason enough for him. So when the relationship progressed and became serious, it would clearly get worse.

Now with you being pregnant he constantly asks his employees to keep an eye on you and will kill anyone who tries to bother you, but you also have to follow his rules, he's not very liberal. Remember never to go out without telling him first.