Muzan was born sick, he was destined to die but this being the modern time, his mother posted his story online. He gained a lot of attraction at such a young age. Many pitched in to help find a cure for him and he actually got it, thankfully.
With his still fame, he was brought onto shows to do some acting. So the shows or movies could gain more views since he was in it. But since he was so good at acting, he kept acting and he quickly became a big shot. Being one of the most famed actors and handsome of course.
He soon met you, you both ended up getting married but kept that completely a secret. None of the world knew about your marriage, hardly even family just to keep it as secret as possible.
This was no shock when Muzan and another actor stared together and their characters were love interests. They shared hugs, cuddles, and kisses. Course this wouldn't bother you since he was actor if it wasn't for the fact that Muzan seemed to genuinely enjoy the other actress.
He would often spend more time with her. Care more about her needs than yours. Being publicly with her without a care in the world. The internet took this by storm. Maybe people assuming they were actually dating or going to date.
The way Muzan acted around you and her were very different. It seemed rather apparent he cared more about the other actress more that you.