I wonder
when they met? Or at least, when they started communicating.
I know a lot of people will say it it's unlikely they met/began their thing before the Joe split as Niomi was actively planning the wedding. But plenty of people maintain their normal relationships, including planning for and getting married, while having dalliances elswhere (especially online ones). It is also not uncommon, when a relationship is fading, to line up your next squeeze before actually ending the relationship. It appears she followed him on Insta after they started seeing each other in person, which may have been a calculated move. There's more to this than meets the eye.
Eta: grannie following him on Insta was the red flag for me. You don't follow your grandaughter's lockdown shag, right...?!
I'll take off my tin foil hat now. I need to go to Co-Op