I thought they was gonna end it off with them having a baby at least 😔✊

We don't know for sure that they could make babies together though.
That guy said biters and nectar could make babies that were (almost?) guarantied to be biters as well, which is desirous as most biters are born only every second generation. After that he points out that anna (a male) is the only biter in his house and he wondered why they were trying to conceal a MALE nectar - indicating that mitsuru shouldn't really be that important to anna unless they were dating.