I agree, it is odd, but I think it may be part of the "keeping the relationship low-profile" thing. Them following each other would make it obvious that there is something going on (although Terry and Verity may not want to follow him anyway). I think many people on Instagram and Youtube are not aware that Niomi is engaged (lol) again.
I also agree about the supposed honeymoon stage, how does that work at such close quarters? Maybe they have been together longer than we know. And Niomi never struck us as a sex fiend, so maybe things have calmed down already. :-I